I regret your MIL's condition. You are a good DIL.
Truthfully, on some level, I relate to you. Several years ago, I deferred getting a yorkie, too. There was a lot going on in our lives, and we were considering re-locating. Getting a yorkie was not a good idea, as much as I wanted one.
A couple of years ago, I joined YorkieTalk. I didn't even own a yorkie yet. As fate had it, I found my yorkie on this website. Also, we were in a good place in our lives to have a yorkie (finally).
And you know what? Tatiana was EVERYTHING I hoped for. She was my dream dog. If I had to do everything all over again (like defer getting a yorkie), I would not change a thing. Tatiana was worth the wait!
I hope the same for you.