I know people like this. She needs counselling. This can't be dealt with logically b/c her fear isn't rational. You can't help her. She is going to self-sabotage until she faces whatever issues she has about relationships and trust. She may recover from this but it will happen again. This is not a relationship you will ever be safe and comfortable in.
Trust = comes from her
Trustworthy = comes from you. You sound trustworthy, so it's in her court what to do.
Take care of yourself. Find someone emotionally intact. Good luck.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh