If her teeth are in bad shape, that can actually contribute to health issues, so cleaning them is a good idea.

How long ago did your vet pull blood? If it has been more than 3 months, I would have it done again. 12 is a geriatric dog and even though for a human 3 months isn't long, it is for a dog, especially an older one. I know it costs money but a blood panel can tell the vet so many things, especially since her kidneys have already shown some issues.

In general, anesthesia is safe and your vet wouldn't not suggest it if he or she didn't feel it was going to be safe for your dog. Of course, there are always risks, but there is risk in everything.

Good luck and good for you for being a good dog mom by asking questions.