You are unlikely to collect a dime, so don't worry about how big of a judgment you can get.

Collect 6-8-12 months or more of rent. 

We use Myrental.com to do all our background checks and collect ID and pay stubs from there.

They're not going to close the deal without the money for current taxes due being collected, so you don't have to worry about it.

Worse, they could put the collection on both of your credit reports, which could show for 7 years even if paid.  

I'm so glad I took the leap of faith and now have a couple of rentals.

They would not do anything and just collect the check for the sale.

I hope that this “role play” makes sense for anyone else - the point is not to assume something that is not actually in the law, because it may show you acting in bad faith if properly spun by the other side, despite your reasonable desire to want to have evidence.

If the state has held a Certificate of Sale less than three years from the date of sale by the county tax collection official, the Certificate will be assigned to the purchaser.

Unless she's breaking some rules, don't do anything but collect monthly rent.