In my novel, my protagonist joins a team with four other characters to go on a quest. Each character in the team is supposed to contribute to the journey in someway and all are mentioned in a prophecy. I've got all the other characters down in my head (their personalities, professions and roles) but for one character in the team, I'm totally lost. I have done so many character charts but they don't seem to help. When I'm writing about the character in a chapter, I don't struggle but once I try to actually formulate and outline things such as what she does for a living or what kind of person she is or what her voice is, I lose her entirely. Sometimes the more I solidify one character, I lose this one more and more. My perception of her is constantly changing so that nothing actually sticks in my mind. I've gone to other writing blogs for advice on this matter and they suggest cutting the character out entirely but I don't want to do this at all. I don't know what to do and it's halting the progress of my novel completely because I keep getting stuck on this one character. It's nearly convincing me that I don't have enough imagination to do this at all.
When I have trouble finding a character's voice or personality, I tend to go through a process of interviewing characters ... literally. I write a scene where they come in and discuss who they are, and why they're the right character for the story. If they're not convincing, I'll do it again, with a slightly different character, until they seem right.
The results are sometimes a little odd. Many characters don't like being pulled out of their ordinary lives and treated that way. It's not like they want to be in a book anyway, really... but that's fine. They don't have to actually cooperate with the interviewer. They just need to show who they are.
Other things to consider are that for this kind of story, where you're building a team, every character has to fit in with the team in a useful way. That's not just to say that each character provides talents that the team will need to finish their task: they also all need to provide conflicts that will make the process interesting, flaws that differentiate them from the rest of the team (and which can be countered by the others, so that the team doesn't actually fall apart because of them), and probably even it would be helpful if their personalities complement other team members. If one team member is quiet, it's useful if one is a little too loud. If there's a team member who doesn't quite understand why he's there, then having one who is particularly clued in could be a good idea too. And so on. So perhaps the reason you're having trouble with this character is that she doesn't complement the rest of the team in a way that's useful. Try to see which of the other characters could be her opposite in some way. Or make her opposite to all of the others, just in different ways.
And never forget to make sure everyone has plenty of conflict. :)
Perhaps this character "wants" to be someone quite different than you are trying to make her be. It sounds like she's making a mystery of herself. Perhaps this means she isn't who she claims to be. Perhaps she's in disguise, or an amnesiac, or enchanted, or an imposter, or hiding a big secret. Or maybe she just doesn't want to be as tightly controlled as are your other characters. She wants to retain the ability to surprise.
In the larger picture, you should ask yourself why this character is so important to you, and if her importance serves the book. Maybe she belongs in a different book, or in a different role in this book. If not, then maybe the fact you are getting hung up on her means that there's something fundamental about this book that you need to change --or about your approach to writing. Writers are often divided into "planners" and "discovery" writers, but it's perfectly okay --and arguably better --to be a bit of both. In my current book project, most of the characters were carefully planned, but some of my favorites weren't planned at all --I learned their backstories only after I had written their parts. Maybe this character is bringing you a bit of much needed anarchy or chaos.
Finally, it's entirely possible that it might be best for your book to eliminate this character, and I do think you need to embrace that possibility. In art, as we are so often reminded, we need to sometimes make tough choices to serve the larger story, not our personal attachments.
Adding to Jules excellent answer, consider writing a funeral scene for the misfitting character, allowing each his teammates to speak on his behalf. Have them tell anecdotes about him and admit to the parts of him that really annoyed them. Find one distinct reason why each member of the team valued him and was (maybe secretly) glad that he came along.
Then, when things are getting too sweet and sappy, have one character drop the pretense and offer a darker, more anger-filled tale from their relationship to the deceased. Have them storm out of the funeral and then let each of the remaining team mates respond to the outburst, either by chasing the angry one or staying to rebut the accusations and defend the honor of the misfit.
All of this will hopefully reveal hidden dynamics about everyone in the team, while also fleshing out the misfit and finding some ways to for him to fit in. Then when you are done with the funeral scene, file it away with all your other characters sheets and plot diagrams. These pages are not for your readers, they are just for you; to help you learn who your characters really are.
Since you are writing a group, consider what character traits are missing in the group without the character you're struggling to write. Does your group have a comic-relief? A moral compass? A quiet steady person? Etc.
Remember also that opposing traits make each character stand out: like Spock and McCoy in Star Trek bouncing off each other. So, once you have a "moral compass" character, get a character who is comfortable with a "means justify the end" attitude. Once you have someone light-hearted, get someone serious, uptight, and intent on the goal. Once you have someone quiet and steady, get someone impulsive.
Each of your characters needs to have their unique place in the group, need to be taking actions that cannot be taken by any other character. Otherwise, they're not necessary, they're replaceable by the characters already there. Therefore, look at what's missing in your team, and construct your character off that.
Perhaps it would help for you to list what your character is not.
Try to think of traits she doesn't have. What professional skills does she lack? Is she not a fighter, not a tech, not a magician?
Is she not a leader? Is she not a peacemaker? Is she not clever? Is she not attractive, or sexy? Is she not a good liar? Is she intelligent enough, but not creative? Or vice versa? Is she not careful? Is she not emotional? Is she not respectful of authority?
There are many more things to NOT be than there things TO be, but every thing she is NOT narrows down what she IS.
In the end, you don't have to have a character profile, you can work with an anti-profile: Here are the things she will not do, and her actions will be consistent with that.
Personally I don't use character profiles. I know many people that I can predict their actions, without putting exactly what I know into words, except for very specific things like Josh hates salads or Kyle likes action movies. Lana will go thirsty for hours before drinking water, she will only drink something flavored.
These are not "traits", exactly, just what they like or enjoy, what they don't like, specific types of things that make them upset, or laugh, or bore them to tears.
Work with that, and don't try to generalize it. You will get a sense of her without labeling what she is.
I've never done character charts. When I want to get to know a character better I put them in a bunch of scenes. They're in a conversation with their boss while they have a stone in their shoe. They're flirting with someone while drunk. They get pulled over for speeding and they're late for their wedding. Whatever. Put them in a scene with another character or with someone who's not even part of your story. Just write and see what they do.
Then, once you have a draft of your story, ask your readers what they think of the character. Their insights will likely reveal things about the character you hadn't noticed.
Write from their POV
This is basically the same solution as everyone else has provided, and can actually be combined with most of them. Pick a scene - be it an out of world interview, or a scene you've already written, or a story from the character's past, and write that story from the point of view of your problem character. First Person POV is ideal, because it gets you into their head that much more intimately.
Don't worry if the voice wanders at first - it's not like you're planning on publishing this anyways. Continue to explore the character until it starts to click.