As for feeding three times per day, if your schedule permits it, go for it. Many cats do just fine on two feedings per day but they will be happier with smaller more frequent meals.
Again, talk to your vet first to rule out medical issues and get their thoughts on if and how you should change your cat’s diet.
Before changing anything, talk to your vet. There are conditions that can cause your cat to put on weight and your vet may want to check on that.
You could well be right that her getting spayed was a trigger in putting on weight, though. Cats’ metabolisms can slow down after being spayed or neutered resulting in them burning 20-30% fewer calories. Feeding the same amount after spaying as before can cause your cat to gain weight. You might try reducing the quantity per feeding or switching to a less calorie-dense feed.
As for feeding three times per day, if your schedule permits it, go for it. Many cats do just fine on two feedings per day but they will be happier with smaller more frequent meals.
Again, talk to your vet first to rule out medical issues and get their thoughts on if and how you should change your cat’s diet.