every snake poops at different intervals, but if you think that she is dehydrated and should poo, then just give her a warm water bath- that will help loosen anything inside her and should help her poo.
We just had a snake that looked like he needed to poo (he was reallllllly round) and didn't for a few weeks, and a couple of days after a nice bath he pretty much expolded... and did seem to be feeling a lot better after.