If reconciliation is possible I'd like her to get professional support and set up some boundaries.
Right now I haven't seen her for two months or talked to her for over a month. Haven't heard anything from her either. It could be because she's living a very solitary life supported by her parents so doesn't go out much or have things she needs support doing.
When we do see each other next is there anything I can do to stop devaluement? Should I try to appeal to her or just ignore her if she's still devaluing me?
Anything you do will have some effect but I don't think there's any way to predict. Their view and input from the world is filtered through the NPD mindset, so there's just no saying how they're even understanding the world. And as for trying to stop devaluement just forget it, it will be perceived as manipulation (which it is) and will very likely backfire.
My advice to you is to be yourself, be open and accepting, and see what happens. Also take a mental step back every now and then and consider how things are with respect to reality. My boundaries were so low that I would let alot of stuff happen just because I liked what I felt was acceptance when it was really manipulation.