This is actually really common behavior in autism spectrum kids, and in kids with PTSD (adults as well for that matter). They become completely overwhelmed and melt down, flying apart at the seams... and especially as children become very violent.
One of the most common solutions... holding him... teaching his body to be still until his mind can focus again, is something she's already doing.
There are massive numbers of preventatives, however... most involving limiting the situations which cause the meltdowns. In PTSD cases, it also means slowly and intentionally reintroducing those situations. Aspie/Autistic kids... it depends on the kid. Usually they have be both be a certain age and mental/emotional capacity (varies with the child) so they have more conscious control over their actions, before intentionally introducing stressing stimuli.
Other solutions include things like therapy, OT, sensory rooms, meds, etc.
It sounds like she and her son are already seeing a psychiatrist/psychologist? If she's working with them and they're any good... then she should be on the right track. This can take YEARS though, both with PTSD and autism spec kids.