Bless you both. I really feel for the pair of you. It's clear you care greatly about her and that's lovely. But what the others have said is so true. The only one who can help her is herself. If she doesn't figure out how to get through this and leans on you too much, then she will become reliant on you and never truly overcome this.
I know two years may sound a fair time, but it's still really early days. Suppressing something that awful is a normal reaction for many, it protects what you may not be able to cope with at the time. What she went through will always be with her, but with a little help from a good therapist, your support and of course her own strength (which she has a lot of to have left this other guy) then she will absolutely learn to manage her feelings and learn she can trust again.
Speaking from my own experience, I was in an extremely abusive 'relationship' 16 years ago and I have never dealt with it properly. It really screwed my head up. I tried therapy, plenty of it, but it always ended up too much to cope with so I'd cancel, or the sessions were limited so just when I felt we were making progress they'd stop and I'd feel back at square one again. My previous relationship was right after the nasty one, and we were together 11 years. But because it was so soon after and I'd not sorted myself out, I became reliant on him for everything. It really didn't do me any favours. He was a nice guy and stuck by me, did everything he could to help, but I wasn't doing any of the legwork.
We split, different story.. My husband now after my mental health took a nosedive I've started to become reliant on him too and I don't want to be. Putting things in place not to make the same mistakes again. But do I trust him? No. Not 100% anyway. Very much like your girlfriend, I believe a lot of the time that he will one day abandon me. Or I think he's lying when he says he loves me. I get scared I'll be forced into things I don't want again, even though he's nothing like him at all. It's all ridiculous when I think about it, but applying rational thought is easier said than done when you feel vulnerable. And this is it, when you're in love with someone you are vulnerable to them. It's scary enough for anyone, never mind someone who's been through something terrible with someone they thought loved them. It breaks everything, every bit of trust in people you ever had. What with her dad too, maybe she's thinking history is repeating itself? It's hard not to think like that, even though you may be the complete opposite of those men. It doesn't sound as though you've taken it to heart and sounds like you're well aware of why she's being like this and that's good. It's lovely you're so understanding. But don't forget to look after yourself too. Give her support, a hug, a friend by all means, but she has to do this herself.