A bunny not eating and drinking is always serious, they must have food in their system all the time or their intestines stop moving and the bunny can die.
If it’s just been a few hours and she doesn’t look lethargic or like she’s in pain, there are some things you can try at home. Baby gas drops (simethicone) can be given on suspicion of gas/GI trouble. You give 1 ml every hour for the first 3 hours, then 0,5 ml every 2-3 hours. Many bunny owners including I perceive it as this often helps, but there’s no hard scientific evidence. Baby gas drops is available in supermarkets like Wallmart or in pharmacies.

You can also give a light tummy massage. A bunny that has a tummy ache will often let you massage it’s belly. Here’s a short instruction-video: https://www.youtube.com/watch?v=JnuxGLa2reg

It’s also good if you can get your bunny to move around. Physical “exercise” helps with intestinal movement (peristalsis). Don’t chase her, but try and entice her to hop around some. If she absolutely won’t, just drops down and presses her tummy to the floor (like a push-up), she’s in pain though.

If this doesn’t go away in 12-24 hours, closer to 12 than 24 imo, you need to contact a vet. You bun can need pain-meds, sub Q fluids and perhaps a motility drug.

Keep us posted.

Not to worry you, but when a bunny doesn’t eat or drink, this can turn serious very quickly. Does she seem lethargic or in pain at all. Sometimes bunnies who have gas or digestive issues that are causing discomfort will hunch up, or try to stretch out and go back and forth into different positions within a short period of time. This article is very helpful in identifying some gi issues and gives you some instructions on what to do about it.
http://www.bio.miami.edu/hare/ileus.html

Bam, looks like we are on at the same time — I posted and then saw you just posted! Great advice