In terms of an absolute threshold: If she has not poo’d or eaten in 12 hours, that is considered a medical emergency and she needs to be taken to a vet immediately.
If the cause of not eating is gas-related, there are some at-home measures you can try to help her pass the gas along. Note that if the gas has accumulated to an extent and/or if the cause is not gas, these at-home measures will not be adequate and you need to bring her to a vet: https://wabbitwiki.com/wiki/Gastrointestinal_stasis#At-home_treatment
**One of the most important pieces is force-feeding if it has been several hours since your rabbit last ate; however, you must check if your rabbit has a blockage/bloat first before force-feeding– force-feeding a rabbit who is bloated/has blockage worsens the problem, and rabbits with a blockage must go to a vet immediately since there’s nothing at-home to do for a blockage. The Bloat vs. GI Stasis video in the link is important to both watch and listen to to best assess what is the case.
Hopefully she gets through this episode, and then separately, you will need to talk with a vet and potentially do some assessments to figure out exactly why your rabbit is not eating/drinking as she should. See here for diet information: https://binkybunny.com/infocategory/healthy-diet/ .. it is possible that not only stress, but something medical, such as dental discomfort, is preventing her from eating as she should, and veterinary assessment is needed to understand what’s going on.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.