There might be something in the NY landlord tenant law that allows for breaking the lease due to domestic violence.

Here's the state law:

http://codes.lp.findlaw.com/nycode/RPP/7

And here's the rent stabilization law:

http://www.tenant.net/Rent_Laws/rsc/rsctoc.html

Frankly, if there is an out for domestic violence, your friend will have a hard time evoking it if there was no physical violence.

She does have the option of just packing up and leaving and accepting whatever consequences (like a lawsuit) that might come her way.

The life lesson for today: Roommates are often the kiss of death. Better to live in a small efficiency apartment on your own or with your parents, rather than go the roommate route.