Need PostOffice's "Certificate of Mailing".

This is not Certificated mail. But a certificate to indicate that you have officially mailed this to her. Later on you can use that in court as evidence. In my place the "Pay and Quit" notice allows 5 day for her to pay up. Please don't forget to add 5% late fee in the total owed. After 5 days of mailing and she still doesn't pay up, go to court to file for "Non-payment" suit. Court may schedule hearing in 3 weeks. If you win the case, you can start eviction after that. Do it quickly because each day delay will be a loss to you.

No email. Everything must be in writing.

Next time, check credit report on all applicants. Please search my postings on how to review credit reports. There are many similar posts in my blog too.