Please make sure that your piggy is eating; if necessary hand feed through the night and the next day until she is eating fully by herself. Please check on her over at least once or twice during the course of the first night even if she is eating normally. You won't need to give any meds during the first night (as she's got all that during the op), but ask your vet for some metacam (painkiller) and how soon you can give how much.
In rare cases, guinea pigs can gnaw on their fresh operation wounds. In that case, you need to see an out-of-hours emergency vet asap (your vet receptionist can give you the contact number and address). A little bit of bloody spotting is fairly common during the first post op hours, but it shouldn't be more than that.
Please handle her carefully and don't put any pressure on her belly for the first week. The body will take 2-3 days to settle down after a major op, but the wound should heal within 10-14 days. Weigh daily to make sure that she is eating enough. A sudden loss of appetite/weight during the healing time can indicate an infection, so please have her seen immediately if that is the case.
For hand feeding, you can mush up pellets or feed recovery food (vet should have some), also add some probiotics as your girl will be on antibiotics. Cut the narrow tip off a 1ml syringe (ask your vet for one), just in front of the black plunger. To keep the weight, a piggy needs to eat the equivalent of 120ml in solids or recovery food in small portions over the course of 24 hours. Getting it into a piggy off food can be a bit of a struggle, but every bit helps so please persist! Don't forget to off your girl some water in a syringe with every feed, as much as she will drink. Always try fresh greens first (fresh herbs or scissor cut grass go down best) to encourage her to eat on her own.
Here is more info on post-op care and hand feeding:
http://www.guinealynx.info/postop.html
http://www.guinealynx.info/handfeeding.html
My 5 year old/700g Cariad made through an emergency spay in May with flying colours and didn't lose any weight at all (except for the lost body parts), but I was lucky to have an excellent vet. Cariad was found to have a grossly enlarged, fluid and lump filled borderline pyometric (infectious) womb as well as some rather nasty looking cysts. She's still with me! She started eating by herself at about 3am halfway through the night.
I moved Cariad back in with the elderlies group once Cariad was eating well and was back to her normal self after 2-3 days.