I'm asking because I don't want her to be in pain, but I also don't want to risk losing her so soon if the surgery will be too risky.
This is a personal decision, but my opinion would be to go for the surgery. Bladder stones are very uncomfortable and highly likely to cause even more problems down the road. In veterinary medicine today, the precautions used during surgery are amazing.
Your vet will likely perform a blood test prior to surgery to make sure her liver and kidneys are functions well enough to handle anesthesia. She'll be monitored closely during surgery by both a technician and monitoring equipment. I've seen many older dogs survive surgery and feel much better afterward.
Your vet is recommending having her spayed while she's under anesthesia to prevent her from developing an infection in her uterus called pyometra. If she would develop this at her age, it would be devastating. She'd also need an emergency surgery.
Best to have everything taken care of at once while she's asleep!
If your dog is 14 yrs. Old there are risks to have an operation at that age. At the same time there are risks of have urinary stones too.
I would consult your vet and get his/her opinion of the situation. Give it some time to brew so you can think over the options they have given you. They might have another safer way to remove the stones without having to put your dog under.
One of the big risks of putting an older dog under and that the heart might give out depending on how weak or strong the heart is. Another is oxygen levels. If not enough oxygen in the blood stream, then he/she will not be able to have the surgery.
Again I would talk to your vet and see what they have to say. I wish you and your dog the best of luck in the world. I have seen that case many times and every time it has turned out differently.
Keep your head up and think the best. My prayers are with your and your dog, Annie The Pet Nanny.