So keep fat margins in all of your estimates. 

For all you know, she'll decide she wants another 18 days and another 18 days ad infinitum.So, just let her know you will not be extending the lease, and will be happy to accommodate her with an eviction on her record, and a nice fat judgment to go with it, if she wants to play nasty.You're going to be out money on this tenant no matter what, I'd bet.  

They had a legal contract and obligation and broke it, leaving you in a big bind.  

I need to cut the fat.  

Crack isn't a joke and might put you in legal bind if other tenants find out you knew about his past run-ins.

Nice bluff, is my opinion.Because when they accepted money from you, they formed a binding contract.  

There's no legally binding contract. 

A judge may accept a text message from the tenant as proof, but they are not binding in court and I wouldn't hold my breath about it.

Last thing you want is this guy thinking that you are ruining his life or putting him in a bind.

Once you have made an exception for one then you can get yourself in a bind with legal issues such as discrimination suit on the next perso who you deny with similiar backgrounds.