
Bitches do not have a menopause so are never really barren, though as this case shows a bitch having a later first litter can lead to problems not least of which is poor mothering instinct.
How old is the bitch that she fears a GA for a spay, I don't understand why did the owner not have her spayed years ago if planned breeding was a non starter, especially with silent seasons. I have all my girls spayed after their last litters, usually the spay is around 7 years of age, and they positively bounce back.
Spaying when the pups are around 12 weeks old is the best option for this bitch in my opinion, safer than other contraceptive methods which might lead to Pyometra and an emergency spay on a very sick bitch.