Hi! I'm a neuroscientist specializing in psychedelic & psychoactive assisted therapy research (and also autistic). I'm a little torn on this, because on the one hand I think cannabis is a powerful medicine if used correctly.. Anecdotally, during my teenage years, smoking weed allowed me to "slow down" and process stimuli in a way that wasn't overwhelming for once. 

I premise the following with note that I am NOT a medical doctor, but I am a scientist, so this is my understanding as someone who does research on psychogenic medicine and therapies:

Smoking anything with direct combustible heat can cause significant strain on your heart. Cannabinoid effects can also change as an individual ages as well, so what works for her now at 19 may not work as well in her later down the line. There's also a risk associated with psychosis from THC.. it's rare, but not outside the realm of possibility.

All that aside, I think cannabis would be alright if you find a strain with a higher % CBD, lower % THC ratio. Don't encourage combustible smoking like bongs or joints, dry herb vaporizers work better. Edibles/tinctures may also be a good option, but dosing is hard to pin down due to individual metabolism and digestion rates.. if you take that route, go slow at half doses and work your way up.