If she's eaten three times, it's been about three weeks, yeah? No worries, yet. They can go for awhile before they take a poo. Sometimes a month, sometimes more.

Giving a good soak will help loosen things up, though, if you get worried. Fill up a tub of some kind about half as high as the snake's girth with warm water. Put the snake in the tub, seal it, and let her soak for a good thirty minutes. P.S. This also helps with shedding