As it stands, if she refuses to leave you can talk to the police about having her removed as a trespasser. I suspect, though, that when they hear that this is your ex- they will tell you that it's a civil matter and you have to evict her - but you won't know that until you ask. (If it needs to be said, this is not an emergency and thus you would not call 911, you would use a non-emergency number or go into the station in person.
The eviction process is outlined
here; your county may have a similar summary.