Have you tried making sex just about her? Maybe instead of regular sex you can give her oral sex until she reaches orgasm? Or maybe if she can pleasure herself with you touching or kissing her.

It could also be a comfort or anxiety thing. If someone is uncomfortable, (which sounds like she is from her past experiences) it may be difficult for her to achieve orgasm. Maybe you could do something to make her feel more comfortable. Maybe a sensual massage. My wife really enjoys a full body massage and it make her feel good about herself. I hope you find something that works for both of you.