OK, this character is a homeless woman (she wanted to be a musician but her career badly flopped and she ran out of money). She got bitten by a vampire and rescued by two superpowered kids (twins). The kids take her back to a cave, then decide to turn her into a vampire and trap her in the cave with the spell. They hold her prisoner for a couple weeks, and then lock a guy in with her and starve her until she kills him. She ends up accidentally turning him into a vampire rather than killing him, which the twins are amused by. A couple days later, they do an experiment that scrambles both prisoners' minds, and she recovers but the guy she turned doesn't. He's left severely brain injured and functioning like a toddler. How will she react when she finds out the guy didn't recover? The twins are telling her to take care of him because they don't want to bother. One thing I thought of was feeling guilty, because he considered resisting the experiment and she encouraged him not to (not all their experiments are dangerous/unpleasant, and she's afraid resisting will get them mad).
Why are you asking us? Do you think someone has personal experience with it they can share? You are the writer. You set up a scenario, and then you [show the readers what comes about as a result! Take a deep breath, and dive into it. Be active, a writer, not a passive sponge or a photocopier.
If anything, she'd be question why she survived and he didnt and would be interested in knowing why. Her feelings towards him would be more a curiousity than guilt. If she isn't embracing her new identity as a vampire than perhaps she is happy he didn't survive the torture. By having her curious, perhaps she can disover what makes her special and that motives her to accept her hero role.
I think that this is a use of the word "rescued" that I'm not familiar with. I'd say that she was kidnapped and tortured by the two superpowered kids, not rescued. It seems to me that her primary motivation would be to escape, her secondary motivation might be to rescue the guy by taking him with her on her escape, and her third, though perhaps most pleasant to think about, goal would be to have revenge on the twins.
I don't know about the questions you asked. I just read your entire manuscript in 150 words, and there's another 20,000+ that I'm missing so I can't say how the character should feel. But I love the idea!
No offense but this summary seems like the kind of story I tell my 4 years old niece and 5 years old nephew... you know, the kind made up of incoherent events coming off the top of my head just to see their reactions. So, this snippet sounds kind of funny to me, but it all depends on how you actually write the story. For all I know you can make this very very scary.
I'd find this vampire boring to read. She's a vampire, for crying out loud - she needs to start fighting. What's driving your story forward, just us reading about how she gets tortured and submitting to everything? Depending on her reaction with regards to this, it would affect her reaction towards the experiment. And it all depends on her personality, and how being a vampire affects her as a person or may have altered her existing personality, maybe amplifying certain aspects. Seeing as we don't know your character, you shouldn't really be asking us. Ask yourself!
