Tenant moved out, someone else is in apartment... What are my options?

[Craig Peterson]

Hi all, hoping for some advice in the following situation.  

I have a rented apartment (Arizona) with one inherited tenant on the lease.  Apparently his girlfriend had been living there as well without being on the lease.  He was late on April rent, then I got a call from the girlfriend saying he moved out and she was still there.  She was wanting to know how to proceed.  My plan was to screen her like any normal tenant, sign a new lease, have her catch up on April rent, and move forward.  Since that call, she has stopped returning all calls and texts.  Rent has not been caught up.  I started eviction paperwork for the original tenant even though he's physically gone.

What are the next steps with the girlfriend since she's not on the lease?  Is she technically trespassing?  Do I put a notice to enter on the door then change the locks?  What are my options?

Thanks so much if you've been through this and have advice!