I can't speak for your specific situation, but.... I have learned that I cannot count on my water bottles actually providing enough water for them. I recently found that all my bottles were leaking... giving me the perception that the rabbits were drinking enough. When I suspected this, I offered water crocks, refilled a few times per day. The rabbits all drank more and all gained significant weight. This tells me that, even though they were getting some water, it was not enough to keep them healthy. Not sure if your water bottle might have been the issue. But it does happen fairly quickly, IMO.
I'm mentioning this because I lost a rabbit a year ago, and never understood why, until now. Looking back, I'm sure it was the water bottle problem.
In a typical cage, one might observe this quicker, but mine are in a colony and it was very difficult to see a controlled status on each rabbit. I've learned, though. And now all is well.
Was your rabbit's breathing raspy at all? Was she sneezing or coughing?