Domestic violence/ child custody with parents who are citizens of different countries

Does anyone have experience with domestic violence/child custody situations where parents have citizenship in different countries?

A friend of mine is in the US on a student visa, her partner is a citizen of the US and he is abusive. She’s leaving with their son and trying to figure out legal stuff, babe does not have dual citizenship yet.

We’re seeking legal help with an advocate but don’t have answers yet, just wondering if anyone here can shed light on the subject?