What a terrible situation Lavazza1st
Because I was an ESOL teacher for many years, I know the Chinese authorities were constantly seeking teachers - I could have made my fortune had I not had 2 little boys of my own to take care of.
So I'm aware there are thousands of non-Chinese men from NZ, Canada, Australia, UK and USA, now with Chinese wives.
Just the difference in the two cultures makes it very hard but for someone with a MH problem it must be even worse.
This, however, sounds genetic, as you feared.
In the end, worried though you are, there is little you can do.
Comfort yourself with the fact that she's in her own, familiar country (unlike your other dil when she had issues in the UK) and surrounded by her family who will, I hope, contact their authorities if your son oversteps the boundaries.
I wish you well.
Having been through it once, I am sure you're now quite philosophical about culture-mix marriages.