Is she moulting? This is when they shed out the coat to grow a new on that is better suited to the changing weather. The fur can come out in clumps, but there is usually not bald spots if the fur comes out easily. Moulting will mean lots of fur around the house, so it is a good idea to brush her often to help control it.
She could be pulling fur to make a nest. This is usually when they are pregnant, but can also be a false pregnancy. The fur is usually taken from the chest (dewlap if she has one). She should be putting it somewhere in the cage and may also be using hay or other bedding in with it. Knowing if she is spayed, how old she is and if she has had any possible contact with an intact or recently (less that 6 weeks) neutered male in the last month.