Evidence of a downward trend line suggest that you may have to plan and execute an exit.

Only facts and evidence.

One idea I'm toying with right now is to ask the tenant to retain her own pest control services and to send me the bill if they find evidence of a rodent problem, but I'm not sure if that's legally defensible.  

The invoice becomes evidence later.Unless you have local weather issues, leave the windows as-is, take pictures to go with invoice.?

I don't know who accepts what type of payments because I don't work with any of the bureaus, but I can screenshot my TU report if you want evidence. :)Originally posted by @Rick S.: Disclaimer: I work for a rent payment service@Nathan Seltzer look into a rent payment service that will process the payments electronically and report the payments to the credit bureaus as I would imagine that may cost less than RentalKharma charges for just reporting payments.

While you may sue the manufacturer, evidence of your own negligence in handling the lawn mower could reduce your recovery or prevent you from recovering any money at all." - See more at: http://blogs.findlaw.com/injured/2015/06/lawn-mower-injuries-can-you-sue.html#sthash.uowiSPqJ.dpuf

Does anyone know what my rights are as a landlord in this situation and how I can get the evidence needed for the purpose of the court hearing.

Any court would require some evidence or proof.  

If the plumber found evidence of tampering or negligence you have a pretty clear cut case to charge her any amount you see fit.

:O)     And if you have any pictures or evidence that the family came and took stuff, keep it; you might need it.