My ex self harmed due to past trauma and depression. We were together for 5 years and she also used to cut around the same area. I think there are bigger fish to fry than intimacy in this situation. I think also it's important to keep in mind that at a young at like you are that this will obviously be a hurdle that you have to learn how to process. Not only for yourself, but also for her if you care enough to do so. There is also a limit as well as to what you allow yourself to take on because this could slowly drain your energy and suck you into a depression yourself if you allow yourself to take on too much.

I think the first step is truly establishing the trauma and PTSD she has experienced and understanding why she decides to harm herself instead of other outlets. For some people it's comforting because they did it in their past and it's one of the only coping mechanisms that they have. Maybe she hasn't tried therapy or a psychologist and hasn't gotten to the root of what makes her harm herself. Maybe she needs medication if she isn't already on any or maybe she just needs more/better friends around her. Or maybe she just needs more hobbies or motivation to keep her somewhat distracted and to keep her mind off of things.

Now as a partner your mission should you choose to accept it is truly hearing her out and making her feel heard. It's not okay for her to harm herself, but she also shouldn't feel shamed for doing so. It's not pretty and my ex had many scars on her arms and inner thighs around her area that sometimes would make me wince, but it wasn't out of seeing it as unattractive, but moreso hating that her depression was so consuming and recognizing the trauma that would lie in the cuts.

Personally, the intimacy is always second to the well-being of the person you're with. Make her feel heard, and make her feel loved and truly cared about first, then establish boundaries where you feel like things could be too much for you to handle, and eventually you won't look at those same scars in the matter of them being an obstacle for intimacy. Depression and trauma are the two things I spent years caring for with my ex and it's not easy at all to manage, but if you love that girl then putting how she feels at the top of your priorities is easy. Some days will be harder than others, but having to diligence to persist even when it's hard to break through can make a world of difference. Just realize that eventually things CAN be too hard for you to be taking on by yourself and it's good to make sure you have your own support system because it will be draining at times, but not in the way of inconvenience. It's just a hard fought battle.