The hell of it is, depending on the state, you COULD have to end up going through formal eviction procedings to get her out. If you throw her out and her stuff with you, in many states, she can take you to court and get damages...IIRC, here in Kahleeforneeya, it can be $100/day...
"Single lodger in a private residence
A lodger is a person who lives in a room in a house where the owner lives. The owner can enter all areas occupied by the lodger and has overall control of the house.8 Most lodgers have the same rights as tenants.9
However, in the case of a single lodger in a house where there are no other lodgers, the owner can evict the lodger without using formal eviction proceedings. The owner can give the lodger written notice that the lodger cannot continue to use the room. The amount of notice must be the same as the number of days between rent payments (for example, 30 days). (See "Tenant's notice to end a periodic tenancy".) When the owner has given the lodger proper notice and the time has expired, the lodger has no further right to remain in the owner's house and may be removed as a trespasser."
The fact that she's the gf's family and doesn't pay rent doesn't matter in this in the slightest...if you want her out, give her a formal eviction notice.