Tenant moving out, friend moved in and now won't leave

[Steven Frey]

So a current tenant is leaving and in the process of moving out by end of March.  They had a friend (not on the lease) help them clean up the house and the friend has put in a bed and TV while the tenant was moving to new place out of state.  The tenant had told them they could stay until the end of the month.

Tenant has shut off water, power, etc starting on Monday.  So maybe the guy will just get out, but he has put a new lock on the bedroom he took over and installed a mega TV she says.

Police came out because they had a fight, but police that since he put a lock on the bedroom, it wasn't their concern.  The tenant is being helpful about everything.

Can the tenant start the evict process (she offered to pay for that...and I have a security deposit), or should I just wait to see what happens, or start eviction?  I don't know how it works for someone that isn't on the lease.