how much should hedgehogs generally sleep?

My hedgehog seems to spend the majority of her time sleeping. Often she'll come out when we feed her, eat, run (slowly) on her wheel (interspersed w/ walking around the cage) for a bit, then shortly thereafter go back into her cave (the thing she sleeps in) and sleep. I stay up late (w/ the lights off for her) and really she doesn't run/explore/whatever for very long before going back into her cave to presumably sleep.When I get up in the morning, it seems as though she hasn't come back out because her wheel will look the same as it did when she got off it. She seems fine otherwise. Is she just a lazy hedgie? Or is it normal for hedgehogs to sleep upwards of 20 hours a day?

*btw, it isn't the temperature, as it's definitely warm enough for her, and this isn't a new or sudden occurrence

*edit* she's not a baby, she's about a year old