Spaying and neutering can have both positive and negative health consequences. I think you’re smart to be thinking carefully about your options, although I would certainly encourage you to go beyond the internet and talk to your vet (which you say you plan to do anyways!).
You can certainly prevent her breeding with careful management. Heck, I know people with tiny dogs who never even step foot outside the apartment much less run free.
For example, the risks of an older dog developing mammary cancer are already there. You’ve missed the window of spaying before the first or second heat cycles, which is when you get the most decrease in risk. Her mammary tissue has already been exposed to a lot of hormones. You can prevent the tissue from being exposed to more hormones by removing the ovaries now, but a large portion of the damage has already been done.
You can eliminate the risk of pyometra (aka uterine infection) by removing the uterus. But you can eliminate the risk of any organ being infected by removing that organ. I agree that it makes sense to look into statistics before making a decision.
You can do some research on Google Scholar, definitely talk to your veterinarian, and you can even consult with a board-certified veterinary surgeon if you want their opinion. There are also veterinary specialists in reproduction, who are probably some of the most qualified to give you advice on this.
I would be surprised if she would be a good candidate for laparoscopic surgery, given how tiny you say she is. I would definitely take her to the place with the best anesthesia since you’re so worried. You want someplace where someone’s only job the entire time is to monitor her blood pressure and her breathing and all of the other vitals. (and no, you don’t get that at a place that charges $60 for a spay - just not financially possible)
In the meantime, here are some of the subtle signs of a pyometra (https://www.acvs.org/small-animal/pyometra):
lethargy
depression
anorexia
excessive water intake
excessive urination
pale mucous membranes
bloody vaginal discharge
