Hi Rella. The theory is that the enzymes in pineapple (like papaya) will help break up the mucus that binds the fur together in the GI tract. There are vets and rabbit-savvy individuals that sit on both sides of the fence on this issue. I know it helps my two, and if anything, it makes a nice treat for them. You’ll want to give them either fresh pineapple, or tinned pinapple that is in its own juice and not in syrup. The rule of thumb is no more than 1/2 teaspoon per pound of body weight.
You want to be sure that there is plenty of good quality hay available especially during a heavy shed, fiber is essential in helping to keep the GI tract moving and pushing through and ingested fur in the system. Not to mention that you want to be extra diligent about grooming your rabbit as well. If your bunny is not as active as she used to be there could be something else going on and it may be wise to pay a trip to the vet. What has she been doing differently that makes her not as active? How is she behaving? is she grinding her teeth, is she hunched up in a ball as if in pain, is her abdomen swolen? What is her diet like?
This is something to read, print out, and have on hand regarding GI stasis:
http://www.bio.miami.edu/hare/ileus.html