That is quite odd. Personally I don't believe IBD is kills quickly and other animals would be showing evidence of it as well. It don't look like poisoning to me either (I have only seen images and vids so that is far from certain) but from what I have seen there is a much more issues than what appears to be in your animal. She does have a pregnant look to her. The weak muscles are a problem and the odd way she holds herself as well. Does she have swelling around her vent? It could be bacterial but I am guessing. A vet even with no experience whom is willing to take a look at her will be able to run cultures. I really have no other ideas. I wish I did she is quite a good looking animal. Her not feeding could be a breeding season response. But a weak body is not a good.
I posted before the other videos, it might be poison too perhaps. I am guessing we all are guessing really. I hope that someones guesses are better. sorry.