Bunnies usually are lazy, however, if you have other animals in the house this may be why.  Also, maybe you should get her out more and play with her, she might be afraid, of interaction with humans.  If you can move the cage, I would definitely take her outside on a nice day and let her get some air.  Good-Luck

 Rabbits (we had a ten pounder)By rule the dont like to be held .Is your cage above the ground in a hutch?if so or not make him/her feel real secure. Hold him to your chest and support him with one arm underneath,set him down and reward him with a good rabbit food.If Cage is on ground keep the door open tempt rabbit with treat outside his door.With time he will come out let him run around in a SECURE area he will be happy and healthy ok?

 OK I notice you said your rabbit was a girl.  Which is kinda funny because I had a girl rabbit and she was usually up at night.  I know you might not feel comfortable "forcing" her out of her cage but that is what you need to do since she is gaining weight.  What you do is you pick her up and put her in an area she can run in.  I let my rabbit run on the porch.  Also put the following items out with her food, some water, and some cardboard.  Rabbits are pretty easily entertained. And let her have some free time every day. The more you do it the more she will look forward to it.  Good luck! :)