If this isn't the case and the sibling did receive prior authorization from you, weigh the cost of cash for keys versus eviction and proceed accordingly.

WHO was foreclosing, a bank, an HOA, the taxing authority?

We are needing to fire our Property Manager (PM) ASAP.We have had them for many years, and don't have any official contract with them, or at least a written one that I know of. 

I know there's paypal, but I wanted something a little more official looking.  

It’s official.

When you get into some of these poor communities you'll find yourself super aggressive and difficult tenants but you'll also find some folks who will do what anyone whom they perceive as an authority figure tells them to do without much thought as to whether or not the person was legit or not.

https://www.biggerpockets.com/forums/12/topics/726422-officially-a-real-estate-investor

How about offering to show it to her to prove you are the owner or authorized to rent unit?

No a certificate of title is an official statement of ownership from the State, or sometimes from a city.   

Put the house up for rent, advertise at your local housing authority, and if a gov subsidized tenant applies and you like them rent to them.