In certain circumstances, immigration law does offer an avenue to permanent residence (green card) to foreign nationals married to abusive U.S. citizens or permanent residents. Because these are very difficult cases, your friend should consult with an immigration attorney familiar with VAWA (violence against women act) applications immediately.
The laws regarding battered spouses allow for the adjustment of status of those foreign nationals who can prove abusive relationship with citizen spouses. I am currently working on a very similar case. USCIS requested immense amounts of documentation. Your friend should consult with an immigration attorney who is skilled in VAWA cases to see if she is eligible for the benefit. There may be other ways for her to obtain lawful status depending on her circumstances.