How can I evict my girlfriend from the house that I own?
You can have her removed but you will need to take the necessary legal steps to legally do so. First, you'll need to serve your girlfriend with a "notice to quit". If she refuses to leave, then you'll need to file an "unlawful detainer" action (i.e. eviction lawsuit). If your successful, the judge will issue you a "writ of possession". If she still does not vacated the writ will allow you to have the sheriff remove her if necessary.
At this point, you should consult directly with an attorney who specializes in landlord-tenant cases. They can best advise you as to specific state law. In the meantime, be sure not to undertake any self-help measures, such as changing the locks or removing her things from your home. If you can face legal consequences.
Note: If you are in fear for your safety, then you could have her removed via an order of protection.