The usual dose is 0.2ml per kilo of rabbit for the dog metacam, but speak to your vet tomorrow morning before you give anything.
Try offering her all her favourite treats as well as things like fresh parsley and dandelions, they seem to go down best after operations.
Vets not giving pain relief to take home does make me mad, how can they not expect someone to be in pain the next day after they've cut them open? Just because rabbits don't show pain doesn't mean they don't feel it. Anyway I wish you loads of luck. Keep her warm, but not too hot. Fleeces or towels as bedding are better than hay so she doesn't poke her stomach with the hay as well.