already? wow. i didn’t realize she was old/big enough yet. most importantly… be calm. you trust your vet, everything will be fine. have some of her favorite fragrant veggies (flat-leaf parsley is great for this) to entice her to eat afterwards. make sure to feed her normal amounts all day. is her surgery being done TONIGHT or tomorrow morning? send food along with her so they can continue to feed her. as you know bunnies cannot vomit and should not be fasted. make sure to get pain meds. if the vet does not offer them, ask for them. it is helpful to have them just in case, esp. with girls. it might take her 1-3 days to “be herself” again. if you have any questions or concerns, please post on here, but be prepared that you might have to take her back if she does not start eating again. if you have a small one-level cage or can block off the levels from the NIC condo, i would do that for at least 4-5 days to discourage her from jumping around.
i’m actually really glad you’re doing this before getting the other bun. this is one less thing you’ll have to worry about later, and bonding may go smoother since those hormones won’t be running strong at the time.
http://www.rabbit.org/faq/sections/spay-neuter.html
http://homepage.mac.com/mattocks/morfz/spay.html
http://www.bio.miami.edu/hare/opcare.html