This is actually pretty common for someone who has been through rape. Here's the thing, she needs help w/ a counselor. Yes, things can work out between you two but she needs to feel that you love and want her for HER not for her sex. This is something you must decide for yourself- do you wish to stay and go through the process of healing w/ her, or do you not wish to deal w/ that. Let me explain why I believe the sex was there in the beginning. She didn't love you as much in the beginning. The "intimate" level wasn't there. I actually think she loves you MORE now, and therefore feels a need to w/h something of herself from you because she's afraid that you want her for sex only and not because you deeply love her.
My best advice is this IF you want to stay in this relationship:
-Explain to her that you want to help her and prove to her that you love her beyond just the sex. That you've never wanted to marry a girl for "good sex."
-Explain that you are willing to give her space w/o expectation of sex for a period of time- a "reasonable" period of time. Explain that sex is important to you and an important part of a "whole" relationship. Tell her she is WORTH waiting for. Set a limit of time to go non-sexual- 3-6 months. In that space, she is to get counseling. You should "date" her during this time.. take her out.. hold her hand.. kiss her but don't go further.. cuddle w/ her, but don't go further. Explain that this is her time to get help w/o worrying about avoiding the sex issue w/ you and it's your time to show her that she means more to you than sex. Tell her if this issue can be worked out that you'd like to take the next step w/ her.. no not just sex, but marriage. However, you do not want to "invest" yourself in a marriage that will be w/o sex.
Possibly this girl simply needs to know that you love and want her for her inner spirit and not for the great sex. Possibly, once she understands this at a deep level, and w/ counseling that she'll be able to "go there" again. Also, anti-depressants kill the sex drive of both men and women. See if she can go to lighter dose or if there are medications that could assist her sex drive.
This is an "investment" in time for you. It may not pay off. If after counseling, and you doing ALL YOU CAN by volunteering to go non-sexual for 3-6 months, this problem isn't resolving, I'd seriously consider moving on because when you have a life partner, sex is part of the "coupling" arrangement. It's normal, natural, and okay to want that. To deny your partner sex on a regular basis causes frustration, resentment, and trust me, it WILL break up a relationship down the road.
I'm going to say something here that is not going to be popular but it's the truth.... some men cheat because they are jerks. Other mean cheat because they love their partners and don't want to end the relationship but are NOT getting their needs met sexually. Women who refuse to have sex with their men or make their men jump through hoops for sex cannot expect their men NOT to cheat. It's UNFAIR. I feel sorry for men who are saddled w/ women who they LOVE but are not getting their needs met. Men derive much self-esteem from sex. Plus, it's a NATURAL drive and there is no reason not to have that satisfied in a committed relationship. So, think seriously about this thing.
You sound like a really nice guy. I'd give this relationship 6 months where you voluntarily go non-sexual. Date her during this time. Nurture her. Hold hands. Kiss. No sex. She MUST seek counseling preferrably w/ a female counselor who specializes in PTSD. After 6 months, GO SLOW w/ moving back into sex. Don't just jump her bones the day the 6 months is up. Also, don't always let her know what's coming (excuse the pun). In other words, when you seek to kiss or cuddle, let it end there sometimes. When she questions you, just say "I just wanted to be close to you because I love you. I didn't seek sex tonight."
Another thing... the truth no matter what some women will say... most women enjoy sex about 1X a week. They will usually go w/ the flow 2X a week. This is average. Men and women's sex drives do NOT match. They never have and never will. So, I would not "try" for sex more than 1-2X a week. "Supplement" the rest of the week, if you must.
I hope this helpful.