If she /he is not on the lease and has no mail coming to the home, meaning they have not established residency then you can ask them to leave.
If they receive even one piece of mail there you will have to go through the eviction process.
Best of luck to you!
Kawain Payne, Realtor
Hire them instead of you doing it wrong. Go to work earn your money, bonuses, or contests and pay the professionals. I learned the hard way. You do what you do well, and hire others to do what they do well. Good luck.
I feel for you. Many, many years ago I let a friend stay in a spare room for 3 weeks while her mom was out of state. 5 months later she was still there. I was an owner, not a renter so I didn't have much of an out.....so I helped her find a job and moved her.
I'm not a lawyer, so this isn't legal advice. However, you say she's not on the lease. Check your lease; there's probably a requirement that anyone over the age of 18 be on the lease, and there's probably also some definition of what constitutes a "guest" versus a "tenant." The problem is that, since your name is on the lease, technically you'd be the one in violation.
I'm not even positive--I'm not a lawyer--that you'd have standing to evict your (former) friend. You're not the owner. And you can't prove (with a signed document) that she's a tenant.
Again, with the disclaimer that I'm not a lawyer, your ex-friend may really fall into the category of a trespasser. She's not on your lease, so she's not a tenant of the landlord. You and she have no document establishing that she's a tenant. She's someone, in other words, who's in the property without the permission or agreement of either you or the owner.
Check with a lawyer to sort things out.
Hope that helps.
Good luck working things out