Hi Chris, it was a good idea to try to get her cleaned up as best you can, it is pretty irritating for a bunny’s skin when they have pee or poop matted to their fur, so she might have been struggling because her skin was irritated. A recommended way to clean a bunny is to cradle the bunny over a sink, making sure to support the hind quarters and back, and have someone gently rinse the bunny’s bum area with a very slightly warm stream of water from the faucet. While the person is rinsing they can use their fingers or a paper towel to gently try to remove some of the urine or poops from the fur.
To me, this sounds like a potential dietary issue, is there something new that you have introduced to your bunny’s diet? No matter how large or small a bunny, if they are a healthy weight they should be able to clean themselves, so maybe there is something she is eating that is causing her to gain weight. Often bunnies at the shelter I volunteer at get “poopy butt” which causes a dirty private area – this can be caused by too many calories, maybe from alfalfa based pellets or too many veggies? A typical bunny diet would be unlimited timothy hay (or another grass hay, but not alfalfa), around 1/4 cup of pellets per day, and 2 cups of a dark leafy green. Does this sounds like Norma’s diet?