It sounds like she was honest with you to tell you because of the negative event, she is just not able to be closer with you. You also did the right thing by telling her you were there for her should she want. It’s not anything personal against you as to why she is not able (or ready?) to be your friend- it is that it triggers bad memories. I’d leave her alone and maybe one day it will be different, maybe she will even reach out to you.