If I eat something that has gone bad and I get food poisoning, I might be unable to eat that food for a long time afterwards. Even if I really want to and miss it and am super careful to make sure it's safe. I might feel mildly sick even just from the smell of it. My body is just trying to protect me, and there's nothing inherently wrong with that food, but it sucks. Given time, and in some cases careful cautious introduction, I might be able to get it down again. Had this experience with a pot pie once, and it took a couple years to eat them again, even when I looked at the box and thought I wanted it for dinner.

With people, the reintroduction process feels unfair. It is unfair. You aren't the same person who hurt her, but unfortunately you're introducing similar feelings or experiences. She wants to kiss people again, she liked kissing people in the past, and she wants to kiss you specifically, when she considers you. But when the moment arrives, or she thinks about the moment arriving in reality, her body goes DANGER DANGER because one time she kissed someone and a horrible thing happened.

It's unfair to her, too. This is an unbelievably shitty thing to have to work through. She might even desperately want a relationship with someone kind, like I'm sure you are, but if she isn't able to know how long it will be until you can have the physical relationship you both want, it makes sense that she'd step back from you. This could take years to resolve, or it might never resolve. She might be being kind to you by turning you down, or she might be being selfish because she doesn't think she can handle navigating someone else's feelings while hers are so intense. It's fine if her reason is either, or both.

So, yeah, what she's describing sounds pretty normal for someone with trauma. I hope life treats you both with more kindness and you meet someone who can return your feelings, and she figures out a treatment that helps her find peace.