She already provided a written 30-day notice, then there's probably nothing else you need to do and can file an FED (eviction) with your county court.
Arguably, she could have established a new tenancy in your basement, depending on the terms of your agreement. In which case you may need to provide a new 72-hour notice for non-payment of rent.
My recommendation would be to hire an attorney to complete the eviction, especially if the tenant is living in your basement to keep things as professional and impersonal as possible and to make sure all of your notices are correct and so you don't have to issue them more than once.
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This former tenant may no longer qualify as a tenant (and thus may not have all the rights that go along with being a tenant. You shouldn't take any action on this without consulting with a good landlord-tenant lawyer in the Portland area. But, if this person is no longer a tenant, there would probably be nothing illegal about you simply changing the locks.
Again, do not do anything like this without talking to a lawyer first. If you do this and get it wrong somehow, you can wind up owing a LOT of money - it's not worth it to mess this up.
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