From personal experience, tip-toeing around someone who struggles with behavioral issues will only make things worse. You can’t fix them. No matter how nice and comfortable you make things, something will always be problematic for them and trying to baby and entertain them will only strain your relationship. You’ll get tired of having to constantly figure out what you did wrong and why they reacted negatively to something when it wasn’t your intention. I am appalled that people are telling you to wait while someone slowly slips away.
Tell her what you think. Ask her if she’d be open to counseling. Take her to group therapy and go with her for moral support. After she is comfortable receiving treatment gift her a couple of counseling sessions. Does she work anywhere? If she does, her employer may offer EAP benefits where she can arrange free sessions with a counselor. If they asses that she needs to see a psychological specialist, they will make the recommendation.