Yep, what Vashti said. She will probably never ever get over it without years of therapy. Giving oral reminds her of when she was 12 and powerless, and forced to do something "dirty" by an adult family member. That's a scary memory. I don't mind helping my gf through anything, as long as she wants to work on it. But at her age, I would think she has no clue on how to work through this, even if she gets therapy. It can take many years to understand your own emotional baggage and then deal with it. I've been there.
Sorry I have to be so coarse, but you posted here and I'm thinking of your needs. My money is on the bet that she will not be able to give oral for the next 2-5 years, even if she does get therapy starting tomorrow. Now what will you do?
If you keep bringing it up she will feel guilty she can't give you what you need, and that will make her feel less adequate.
p.s. I've talked to girls who were sexually abused. Some got over it, with therapy, some never did. The fact that she cried when she tried, tells me she is beginning to face her fears. Her crying was when she was letting out all her fear and frustration. That's a good sign. But it's only the beginning of the beginning.
I have a long time interest in psychology, specializing in relationship dynamics for 30 years.
(Please note, we give the best advice we can based on the information given in a post. For better advice, please include the age of all romantic partners.)