tl;dr: Don't worry too much about another person "stealing" your characters. Even if she uses your names and your visual descriptions, chances are that her interpretation of your character are distinctly different from the character you developed in the first place. The problem gets even smaller when you and her use different types of art to work with the character.
Keep in mind that your original character and her interpretation of your ideas are not identical. Unless she is really good at inception, she has changed "your" characters into something that is uniquely hers and distinct from your original creation. If you change your names and alter some of your visual descriptions, I don't think many people will notice.
Additionally, I am not quite clear on what exactly she has done. Has she created portraits of your characters, or written about them? You write that you don't think that your art skills are very good. Fine, stick to writing then. Writing is much less visual, and to me, personally, the details of a character's physical description are almost irrelevant(*). What brings a written character to life, for me, is their personality.
How do they act, and why? What do they love, what do they strive for, what are they willing to sacrifice to reach their goals?
Creating a (written) character is an involved process that takes into account not only the present state of the character, but also where that character came from and a whiff of where it's going. Very good art can hint at these issues, and a good portrait should capture the personality of the portrayed person. Nevertheless, my personal, most likely horribly biased, impression is that a written character is inherently more dynamic: because it is allowed to act and change -- which is usually not true for a portrait (unless you count the portrait of Dorian Gray).
My point here is that graphic arts and writing focus on different aspects of a character. I think it is unlikely that people will recognise her character as yours if you use a different name. As an example, just think of all the Harry Potter fan-art that exists out there. Some of it is amazing, and yet not a single portrait of Sirius exists of which I can say: Yes, that's 100% him.
Lastly, keep in mind that many characters are related to one character archetype or another. Sometimes it's hard to put the exact name of the archetype on the character, but certain personality traits tend to bundle up and form characters that are very similar to each other. I've noticed that about a character of my own that I first wrote about 17 years ago. Once I had worked with him for some time, he developed a very distinct personality that clearly distinguished him from the rest of my characters. Then I read two books, both by German authors as well, both written for young adults, one a successful fantasy trilogy, the other a queer coming-of-age story. Both stories featured a character that I identified almost instantly as the mental twin of my character. (It took me one sentence in one book, and two in the other, which goes to show that the authors did a fine job of precisely capturing their character's personality when first introducing them.) I had never heard of these characters or books before, and I had not published any of my work. These three characters being so alike to each other was pure coincidence. They are all related to a Hermes-like (yes, the god), shapeshifter-type of enigmatic character, and the details just, weirdly, fell into place, right down to hair and eye colours and the existence of defining scars. And the best thing is: When the fantasy trilogy was turned into a movie, "my" character was played by the actor I always had envisioned playing my actual character. Watching this movie is like watching some of my creation coming to live -- which is plain amazing.
The point is this: I believe that certain structures exist, including whole characters, that resonate with us in a way that makes them turn up again and again. While this is not strictly related to your problem, it serves to show that hardly any "creation" is truly original. I rather believe that telling stories and populating them with our characters is our own subjective way of projecting ourselves onto a universal story. It is our interpretation. And because no two people are exactly alike, no two interpretations of the same story -- or character -- can ever be identical.
(*) For years, I was dead-sure the main character in my favourite YA book had black hair. Then a movie was made based on the book, and a light-blond guy played the main character. It was a shock, but I got over it, because the blond actor beautifully captured the personality of the character.