You need to take her to the vet.  Thats one of the signs in a female ferret  for adrenal disease.

I got one for my ferret Scout and put the lid on it so he could try it out,  He freaked out he was so scared I couldnt get him out fast enough.  However he likes to play in it just without the lid on.

I have actually tried it.  I put boh the lids on it and my ferret freaked out.  Now he does like to lay around in it and play but as long as its not closed up.