You will need to confirm with local building dept if you will need continuous insulation. 1) remove siding and install sheathing with insulation adhered to it. 

If it's a high end unit all the big box stores do 0% interest and same/next day instal...

And she even had purchased and installed new curtains for me.

If nothing else works consider changing the locks, installing a lockbox with a key and leave a note explaining they have to call you for access.

I've used Odor-Xit with some success after a deep clean, and sealing with BIN primer, but this was on the subfloor, which I then installed new flooring over. 

Installed new flooring and painted the entire house.

Most of which came from installing HVAC into both units.

When we rehabbed his studio the carpet install guys insisted we needed a hazmat cleanup team & literally walked off the job.We got the place & within 30 months (& after a LOT of work & some structural redesign) we got the property approved as a legal 6-plex & the rents are currently $4900/month.

Sure if they have renters insurance they should file a claim, and you can see if you get lucky and they cover the entire cost  also keep in mind that you’ll probably have mold, so that needs to be remidiated by bleach or something else before new boards are installed  Otherwise, since they are a decent tenant, I’d try to negotiate and work out a compromise with them.

It also helped that we installed it in house.