Oh Janz, do I ever feel for you and the position you've been left in.
To me, the one "saving grace" about all this is that this little one is in good hands with you. It's beyond sad that these people obviously consider her "just a cat".
I think that, were I in that position, I'd take on the mindset that I was the guardian - and deal with whatever might arise as I would with one of my own cats.....and, boy, when those people returned, they'd get a piece of my mind.
You know, EVEN if they had spoken about this when first asking you....
I'm boiling mad - and I'm nowhere near all this!!! I hardly think you're overreacting.
Meantime, if this cat has made it to 20+ with these people:
- darn good genetics...or,
- did she get to 20 just to spite them?....or,
- maybe they've done something right?
Time for an animal communicator! (I'd soooo love to know, I'm almost willing to pay for one!)