Thanks for the reply. I read up extensively last night until I fell asleep (literally). So I ended up putting Elsa in a crate by herself in another room, but with the room door open. I'm going to take her out on a leash so she can go potty and have some food/water. I'm wondering if she'll even be better after 2 weeks or not. Honestly, it's somewhat of a deal breaker if she can't be left unsupervised with the other animals.The answer is NO!
You have a seventeen year old cat that you should not even consider allowing a strange dog near it unsupervised and you are asking way too much from a new dog.
A 17 year old cat can be easily killed. It would take very little. Hindsight is 20/20. Don't let it happen in the first place.