It could be a number of things, but definitely cause to pay attention. The lethargy is worrisome. It sounds like she is in some sort of pain. It could be gas, onset of stasis, or something else. The pooping and cecals are good because it means she isn’t blocked. Is she molting by chance? Have there been any chances to her diet? Is it very hot where you are?
Do you have any baby gas drops (simethicone)? My first action would be to give a tummy rub and some simethicone (as these wont hurt even if it isn’t gas), and keep offering her hay if she will take it from you.
You can also check to see if she’s dehydrated using the skin tenting technique. Grab a good handful of scruff behind her shoulders and pull a tent (don’t pick her up or anything!), and then let it go. If it snaps back slowly, she is dehydrated. You can try offering her extra wet greens if she will eat them.
The last question I have is whether there is an ER vet that sees rabbits anywhere near you?
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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.