Depends. If it's his name only on the deed to the house and she doesn't pay him rent or have any kind of tenancy agreement with him in writing, he probably can evict her. She should consult a lawyer.
Been there and through that and the answer is no. I had my boyfriend call the police on me to get me out of our apartment. Once the police found out how long we had been living together, they told him I had just as much right to be there as he did, especially since I had contributed to rent, even though his name was the only name on the rental agreement. Also landloards have absolutely no power to evict either and for a landloard to evict a tenant anyway, they first have to serve that tenant with papers that they have gotten from the Tribunal. It has to be for a real damn good reason and even then the tenant has the right to appeal before the tribunal. It can be a real hassle, but in the end it could be worth it. Good luck to your friend! I live in Canada by the way, so that is our law here.
In most states, she would qualify as common law and has a right to be there. Do get her out, he will have to go to the local court and file an eviction notice. That usually gives her about 10 days to find another place and he cannot keep any of her stuff. I think it cost about $25 or more to file for eviction, so he may or may not do that. She does need to call the police if he tries to throw her out -- they will back her up about being evicted. Then, she needs to use that 10 days to find another place and NOT tell him where she moving. She does have some rights, and he probably thinks she doesn't or doesn't know it. She might need to talk to a lawyer about her common law status. She might be eligible for half of his community property if he does get her to leave.Esp if they ever presented themselves as married or she ever did anything as Mrs XX, like paying a bill. But she needs to get out before the whole thing goes south and gets violent!
She should get as far away from him as she can as soon as she can!