Being moved to help this person is wonderful, I do want to say - and don't take it the wrong way - to not be attached to ah outcome on your part. Getting involved with another's emotional state and well being can be an act of loving compassion, but if the benefactor becomes emotionally wrapped up in another's state, well they can get wrapped up in it.
That said, I have experience with ptsd, depression and anxiety and have found psilocybin by far the most helpful outside aid to combat it. On a more pharmacological level, micro dosing is an excellent mood elevator /stabilizer and I feel myself lifted out of the physical depression that accompanies my emotional one (i sleep when down) and that allows me to become active and participate in life. My typical regimen is: for 4 days out of a week, take 0.5 grams cubensis. Lay off 3, do again. Those 4 days may not even be consecutive and that number is only an average. One of the great things about it is the unnecessarity of strict dosing regimen. The only constant for me is dose, and the 0.5g is only my personal dose ;what I found works through experimentation.
My supply of mushrooms is spotty at best, an inability to self - produce them and the economic viability of a continuous supply (if that breaks rules mods, let me know, I tried to be careful) is to daunting to keep it up ever for very long. My longest period was several months after a good fall wild harvest. (got my scissors ready for this year, curious what your temperate summer here in Cascadia is going to produce this autumn - I digress. . .)
Larger, psychedelic doses are a different thing, and very rare for me,about once a year. They are tours of my self, through whatever levels my guide (my Higher Self) determines I am bound for. Psilocybin is very gentle with me when I approach it with deep respect, and I find it very beneficial for working out deep emotional issues with the benefit of having the detached compassion for myself that my Higher Self imparts.
This is all of course, my anecdote, and every persons utility of these things is different. I have, as I implied, suffered trauma but nothing anywhere near what your friend has. I am comfortable in the psychedelic realm, and familiar with it, I think that has always helped me with my work with them. So take all this seasoned with salt.
I wish you and your friend peace, it sounds as if you're both in for some stormy weather to get there but if you keep love as your motivator and compassion your tool, you should all be fine. Be good to you.
Sine experientia nihil sufficienter sciri potest -Roger Bacon
*γνῶθι σεαυτόν*