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.

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

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

Any best practices on collecting past due amounts?

Since I am not really changing the main purpose of the property, one source told me it shouldn't apply.Lastly, do make sure you apply for an account to pay your sales (collected by Airbnb and vrbo, but not others) and Tourist Development taxes (you must collect).

MANY MANY scams going on to collect application fees doing exactly that.

Also, focus on 2 years of job/income stability.Class D Properties:Cashflow vs Appreciation: Typically, all cashflow with little, maybe even negative, relative rent & value appreciationVacancy Est: 20%+ should be used to cover nonpayment, evictions & damages.Tenant Pool: majority will have FICO scores under 560, little to no good tradelines, lots of collections & chargeoffs, recent evictions.

Also, focus on 2 years of job/income stability.Class D Properties:Cashflow vs Appreciation: Typically, all cashflow with little, maybe even negative, relative rent & value appreciationVacancy Est: 20%+ should be used to cover nonpayment, evictions & damages.Tenant Pool: majority will have FICO scores under 560, little to no good tradelines, lots of collections & chargeoffs, recent evictions.

If you have more than one LLC, each LLC should have its own set of accounts.Checking: Collect all income here, then use it to pay bills, the mortgage, or maintenance.

For rent collection, my clients use Azibo.