First i'd like you to know that i am not a professional with sources to cite on the subject or anything, but i have come across similar situations amongst friends and co-workers quite a few times if you'd like some real world advice too.
This will take time. based on her trust issues she will have difficulty accepting your apologies no matter what you do. especially if she has retained this trait for most of her life. emotional shutdown is a tricky thing, it will take more than just your efforts to fully pull her out of her shell. usually any family, friends, even co-workers, can all be recruited, so to speak, to help with this. inform them of the situation as minimally as possible and explain the need to treat her kindly and compliment her to build her self-confidence. others trusting their problems to her as well can allow her to feel like she is not alone and speed up the recovery process in some instances.
1. Phases: she will remain in her shell until she feels confident and safe enough to venture out into "trust territory" again. her other problems in life will prohibit this as well.
2. Your involvement: try taking a more "quiet empathizer" kind of standpoint. try not to bring up the conversation or related subjects as much as possible, and if it comes up, try to show her that you're sorry, instead of saying it. your actions and body language will affect her more than your words if words are what she wont allow herself to trust. think of it like...building blocks, you had a "tower" built high and strong. the broken trust is like knocking over the tower. in order to fix things you must rebuild, bit by bit, and you cannot rush it. haste will cause a weak foundation. have patience, and one day you will find this "tower", your relationship, to be stronger than before. growth from ruin. also, if its at all possible, try helping to fix her other problems she's having. this will alleviate stress and allow her to focus on one thing at a time. too many problems can scare one into stasis.
3. Timeline: there is no real estimate that can be made by anyone for everyone id say. we are each individuals, and she will be ready when she's ready. the more patient you are, the quicker she will recover.
Hope this helps