As somebody who has defenses more secure than the pentagon, I can tell you from experience that the best way to get her to open up to you would be to be patient with her and start off as friends for awhile before entering a relationship.

Also it would help to reassure her that you will accept her no matter what and that she shouldn't fear judgement from you. Don't just say it though, actually mean it and be ready to have an open mind and accept any fault she may confess to you in the future.

Finally, be kind, considerate, and love her unconditionally even if you all remain only friends.

It would take awhile to build trust with somebody as damaged as the girl or myself and the only way to really get past the defenses of somebody who is truly damaged is to overwhelm them with love no matter how annoyed or angry her defenses may make you. If you aren't ready to stick it out with her long term and love her no matter what, then it would be best to quit while you're ahead.