I think in regards to personality changes every dog is different and some become calmer while other stay the same. As for weight they do gain weigh once they are fixed, at least from my experience with every female/male animal I've had because their bodies require less calories. Some foods are even marketed to fixed pets with different formulas.
When she comes home it's very important to keep her in her crate or a small small room. The first couple of days I wouldn't even take mine out, just use puppy pads. The fluids they give during surgery may make her pee quite a bit after surgery. It's also really important to stick to what the vet says for recovery, even if she's back to herself early. Wait until after the recheck to let her back into her old routine of running around. If you have the option of take home pain meds, take them! I kept my last girl I spayed on pain meds for at least 3 full days.
Good luck! And let us know how everything goes
She will do just fine!
I think it's great you're thinking ahead and getting her spayed!
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