Has she got a wheel, mine does it to cool down after a run, she lies very still but if you disturb her she acts as normal so it sounds a bit different, she often goes near the bottle or at least on the top plastic levels, often she is awake actually just checked some pictures:
Mine's getting on a bit, bless! But anyway I wouldn't be concerned unless it goes hand in hand with other odd behaviour. Mine usually moves all her bedding out the house and has a nest, but sometimes she'll sleep in the house if it's too warm.