Hello, for your concern. Your hamster could be ageing depending on the age of your hamster. How old is he/she? Hamsters ageing signs could be eating less and drinking less. Spends more time sleeping and the fur colour could be changing as life moves on for him/her.
If it is not the age problem, she might preferring to just stay in her nest and relax and sleep. Hamsters are most active during dawn and dusk but also varies for their personal habits. What is her routine, if she is more active during the night before, then maybe stay up a bit later to see what is going on. You might discover that your hamster might be ok.
Check of Signs of illness. Your hamster could be ill, try to observe more about your hamster and check if any unusual action happens. Watery poo could also be a sign that indicates sickness check for that.
For now, don't be too worried but just keep on checking. Just make sure you do everything right and keep the temperature suitable for your hamster. Good luck!