What you describe is GI stasis, which is a symptom of something else (pretty much always involving pain).
Not eating, drinking and/or pooping for 8-12 hours is a medical emergency for rabbits and requires an *immediate* vet trip. Severely reduced appetite puts them on the verge of stasis and combined with lethargy also demands a vet trip.
If you tell a truly rabbit savvy vet clinic that your rabbit isn't eating, they *will* fit you in that day or refer you to an emergency vet. In other words, don't call and ask for an appointment - call and tell them you have an emergency and need to bring your rabbit in immediately.
Best of luck to you and Coco... I hope she feels better very soon!
By the way, expect the vet to give you pain medicine like metacam and something for gut motility like metoclopramide... And at this point, the vet will probably decide your rabbit should have Sub-Q fluids. You will also need to syringe feed your rabbit. You can get a feeding syringe in the pharmacy section of any store. Some vets (and some pet stores or feed stores) sell critical care... Though it's usually very expensive at a vet compared to what I pay off Amazon. If you can't find or can't afford it, you can put regular pellets in a bowl with water and microwave them just long enough to boil the water. They'll fluff up a lot. Add water as needed to get the right consistency (I usually add ice cubes, simply because it cools the pellet slurry to the right temperature faster).