Rabbits having soft poop can be caused by several things: diet, stress, bacteria, and parasites. With the diet, you want to try and figure out if maybe she ate something recently that has caused the upset, like a new food, or somethng off the floor. If not, is she getting too many carbs and sugars in her diet that is upsetting the balance of her gut flora. If not diet related, has she had something happen recently that has caused her to feel stressed. If both of these are ruled out, then she may have picked up a bacteria or parasite somehow. In which case, she'll need to go to the vet and have a fecal done to determine if there is a bacterial or parasitic problem.
The best thing to do is to stop pellets and treats(sugars, fruit, grain, starches, and carbs of any kind) and feed lots and lots of grass hay. You may even want to stop veggies. You aren't going to need to feed her critical care either, unless she stops eating. If she has loud gurgling coming from her stomach or severe bloating, you'll need to get her to the vet immediately. If she is sitting hunched up or pressing her belly to the floor, and not moving around alot, she may have some stomach discomfort, and giving simethicone may help. But if it's just a mild diet imbalance, hay is the best thing to correct that. If after a couple days the soft poop hasn't cleared up, or her behavior alters and her condition worsens, get her into the vet right away, as there is most likely something more serious going on and she will need meds to clear it up.
