I'm sorry you've gotten such bad news.
I have no experience with spaying, so take my advice with a grain of salt - but it seems like it would be better to get the surgery done sooner, even though she's older? I would think things would just get worse if you wait. But like I said, I could be totally wrong on the risks. Nancy or Kalandra will probably have more experienced and helpful advice for you. Lots of hugs to you and Nara, and I hope you enjoy every moment you have left with her for now. Give her an extra treat from me.