Well, it depends. She (the main character, I assume) is transported into this world. Does she believe it's real? Does she think it's some kind of delusion? Is this a dream she's having in a coma; according to her, not according to the story or author.
If she believes this world is real, as opposed to a game, she would use the totality of her moral compass, as opposed to, "Oh yeah, slavery is horrid. But they're just NPCs in a game I play."
She could perhaps have an interesting conversation with one of the guild NPCs you mentioned, leading her to believe they are too 'lifelike' to be just mindless nobodies, and that could lead to her considering whatever she knows (whether this is factual or not is irrelevant) about slavery as a whole, and perhaps even 'in-game' knowledge about slave camps in this world.
It all depends on how you bring it over, and how the character (not the author) rationalizes these things. I mean. Let's be honest. Human beings aren't always the most consistent in morality, or even in reasoning. So you could have her be totally against killing, but killing the slavers that are (in her eyes) abusing the slaves she means to free? She could pull a Khalesi in heartbeat.
My suggestion, if you want to get really into the psychology behind it, and put your character under the loop? Put yourself in her headspace (in her mind, so to speak) and keep weighing things against each other.
Killing slavers (horrible people) VERSUS saving slaves (victims of their fate).
Letting the enemies' troops starve VERSUS letting my own troops starve by feeding them.
It's in these harsh environs that we truly learn who we are, and using a tale to expose the reader to these kinds of dilemmas are the best way to jolt their minds with a heavy dose of empathy (or impotent rage, so be careful with that).