My dwarf hamster wont eat. is she sick?

i got a fancy russian dwarf hamster named dumpling and i got her a few days ago and shes not eating. shes getting plenty of exercise and drinks plenty of water. shes not pooping solid pellets like my other dwarf hamster. my other dwarf hamster seems fine. shes exercising and eating and drinking normally. i don't think shes got wet tail because her tail isnt wet and her rear isnt wet either.