She would be a month-to-month tenant. You need to give her one month notice for eviction. But I should caution you there is specialized procedure to evict mentally challenged people and older people. I suggest talk to a local attorney for more help.
Only see a licensed attorney before you make any decision. This answer may not be perfect in any given situation. However, more fact may be required by your local attorney. If you are in Las Vegas, you are welcome to send your questions regarding Chapter 7, or 13 to Attorney Malik Ahmad at Malik@lasvegaslawgroup.com or www.fastbankruptcynevada.com or by calling (702) 270-9100. In many cases, we do not charge initial consultation fee.