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Spay day is never fun.
Whatever vet you use, they should have a good surgical protocol. Not all vets do.
For a spay the dog should have an IV placed before surgery. In case of an emergency, medication can be administered without wasting time to place the IV then. She should also get fluids the day of the surgery. The vet should do surgery on a heated surfact because toy breeds lose body heat so quickly. Pain medication should be offered. Pre-op blood work is the best way to go but some feel it isn't necessary. I wouldn't do a routine surgery without it. And the right anesthesia should be used. Isoflurane or sevoflurane are gas and should be used to maintain and an injection of something else to calm the dog enough to intubate. That is probably the most preferred protocol.
Hopefully your vet will be willing to pull any baby teeth that didn't fall out so she doesn't have to go under again.
She might be given an e-collar to wear but several members of YT have found that a baby onesie accomplishes the same thing and it lots more comfortable. It would be okay to use one as long as she doesn't try to get to her incision through it.
She might be lethargic for a few days and her appetite might not be great. The first night she may just lay down and not move. She should urinate by the next day in my opinion and have a bowel movement within about two days. If you can't get her to drink the day after surgery, I'd probably syringe water to her. If she won't eat anything, you could give a small amount of PediaLyte.
She can't run, jump or climb for a least 7-10 days and better yet wait til the stitches come out.
Bather her before surgery because she can't have one til after stitch removal.
If they are making you leave her overnight after surgery, make sure someone is there awake the whole time. If not you might want to refuse to leave her because it is dangerous but so many vets do this.
One more bit of advice...look at the incision when you bring her home so you have something to compare it to over the next week. It's important to check it for redness, swelling...
By the way, your baby is adorable.