I have a dog who's been bitten (but did not die), and I can sympathize with what it's like to have an animal you love attacked. That said, they didn't even want to take the sheep to the emergency vet, and the OP even had to be the one to get a vet out the next day. They obviously did not love this animal. If it was an issue, they should have said so right away. The woman who's dog bit my dog would walk her dog in front of our house, so I never knew when her vicious dog would be out. I told her right away that I had an issue with it - I didn't wait a month and then put her in a tight situation! This is not about legality, this is about revenge. Revenge for an animal they didn't even care about! I find it disgusting.

I would think you would have some legal recourse here, to buy yourself some more time, but I don't really know. I personally would take this as an eviction notice, and generally you have recourse there. Check your lease and the laws in the city/state that you live in. For me, there's not a snowball's chance I would continue to live there.