What kind is she? It could be she has a wool ball. Use a regular cat hairball med. Or dried pinapple or dried Papya. My Angorias used to do this a lot ,although rabbits can get worms it's just not as likely unless they are running around with another animal that has worms.
Age also plays in to it unfortunatly rabbits don't have a huge life expentancy. I'm so amazed at my WeeOne hes a netherland dawrf/Jersey wooly and hes 15 years old .