How long are you leaving her during the day? Is it more than 3-4 hours?
If she isn't left crated very long when this is happening, then it could be that your baby is nervous when you leave. My younger boy always had to poop the minute he was left alone (and he was only left alone 10-20 minutes at a time
). He grew out of it.
Using an xpen and a piddle pad is one solution to the mess.
Keep in mind that the younger and smaller they are, the more they have to go during waking hours.