Really, it's only time and effort that will help her gain some trust back in you. And even then - she might lost trust in you quite quickly over more minor things.

Has she told you why/how it is that she can't trust you now? For me, personally, it would be a two-fold thing: 1, I would always be wondering when you were going to actually decide to leave and 2, it would show me that you were willing to manipulate me and hurt me to get what you wanted. I probably wouldn't stay because I would have absolutely zero trust or respect for the person. (I have really big trust issues). I would also feel like if I did the slightest thing that would upset them.. that it would tip them over and they'd leave me. So I would probably cut my losses.

She hasn't done that, so that is a good sign. You'll just have to be patient as she will likely get very upset with you over very little things - that tends to happen when you have no more trust in someone.