Your friend sounds like she is indeed influenced by a psychological incapicitation such similar to
the "battered wife syndrome". Considering the environment she grew up in, this is not surprsing.
1) She needs help from those familiar with battered women, such as Domestic Violence Coalition. Someone
familiar with such emotional paralysis can assist her to see why she chooses to stay in such a dangerous
and abusive situation.
2) She is 18. SHE can press charges against the abuser. It doesn't matter what the mother says or does. The next time she is hit, with a bloody lip, bruises,
etc, that's it. That is legal evidence. All she has to do is call the police and say, "He assaulted me. Here is
bruise/mark etc. They MUST arrrest him. San Francisco may have strong laws this way. DVC can assist here
as well with information. Of course, she should do this AFTER she knows she can be safe from his abuse.
Like the day AFTER she moves out.
3) How sick is the guy? Psychopath? Narcissist? Alcoholic? Drug abuser? If he is the average bully...they
respond to fear. As Al Capone said, "People who got no respect, respect one thing; fear"
I once heard of a woman who's ex-husband was stalking her, threatening her life, calling her...this was
in New York...1970's. Somebody she worked with said, "Don't worry, I'll take care of it. What's his name?"
The abuse stopped. Evidently, someone had called this guy up and said, very calmly, plainly, simply;
"Call her again and they'll find you floating in the East River"
Of course, in many states, like California, this is called "making a terroristic threat" and is itself a
crime. Of course, if someone were to call him concerned about his health...saying that this girl had
very powerfull friends who were very angry at him...and he should be very carefull next time he crosses the
street, or goes out at night...that he and his behavior were being watched very carefully...
Good luck. Very painfull situation for her and her friends. Professional assistance and information would be most helpfull.