Help! How do I get an ex-girlfriend to leave? She does not pay rent and is not on the lease

Get her involved with the cops. They will get her out.

That didn't help. They told me because this is her legal mailing address and residence they would just bring her back here.

Hmmm...

I really don't know what to tell you then.

You must start legal eviction process on her to get her out legally.