As far as surgery goes, a 9 year old toy dog isn’t as much at risk as a 9 year old golden retriever. Depending on the dog’s health, they can double their age and live to 18! Then they would definitely be a senior.
The only thing you’d want to worry about by NOT getting the surgery, is the risk of pyometra. Your 9 year old intact female is definitely at the age where she can develop a fatal infection in her uterus. Fortunately it can be fixed via surgery, but it’s like 10 times the cost of spaying her – which prevents it completely.
Does anyone have suggestions via experience?