Oh, what a sad thread. I'm so sorry to read this.
I wanted to reply earlier, but I've been a bit snowed under with work this weekend.
For me it's a way of managing what seem like some very full on, overwhelming feelings.
I've been in a few situations in my life (starting when I was very young, before I could even remember) where things felt very much out of my control and I felt really unsafe. So fear, for sure, and confusion where the world has never felt like a particularly safe place. It's a way of managing those seemingly unmanageable things.
Rejection is a big one for me. Again, from before I can remember probably. As an adult, I can find other people's actions both completely logical and totally true to who they are, but at the same time I can find them completely confusing emotionally for me, and also at times overwhelming. Those two things can be true at the same moment in time, they can run along parallel tracks to each other, if you like.
Also, more recently, anger. After having found a voice to express what I might need in that moment, in a very down to earth and direct way, straight to the point, when that's over ruled or ignored, that seems to trigger a wave of overwhelming anger. I think that's more recent and probably linked to the PTSD though.
Anyway, how to help in your situation? I guess knowledge is helpful. I'm one of those people that finds a huge amount of solace in finding stuff out and reading about it. If I can get the intellectual framework of things, I know I'm on my way to clearing the fog. I don't know if you're like that as well?
Also, for me a huge worry is the thought (and/or reality) of having to manage and deal with other people's reactions. That then ends us being a distraction from concentrating on myself and of being able to pull myself forwards into something more positive. I can instantly sense when there is a good boundary there, and someone is empathetic towards me/my experience, but able to 'leave the emotional space between us clear', if you like. Likewise, I can instantly sense when someone's sense of self is getting tangled with my own. And that's not a good situation for either person.
So, if you can, try to cultivate a sense of 'loving detachment', where you care and are supportive, but there are boundaries there and a good sense of space between you both.
You don't have to talk about 'issues' or 'feelings'. There quite high pressure things to talk about for me and it makes me super uncomfortable and stressed out, especially with people I am close to (although I can be super articulate with medical professionals about these things - I guess I've learned the lingo).
Maybe you could just chat about trivialities, like about what's been happening during the day, or take turns to read out loud to each other. I find those things amazingly comforting and soothing. Other saving graces for me have been to do with finding the things I'm interested in and learning to cultivate and pursue those. I don't know, would she be interested in one of those mindfulness colouring books? Or experimenting with makeup? Even if it's just something like nail polish, or nail art? I always really liked my hands and my fingers (both really small), so I found it very relaxing and satisfying to look after those and see them looking their best, even when I felt low.
Hope that helps x