OP--have you considered outside training? With your schedule the way it is, it sounds like you might do well trying that. When they go outside, they learn that no where in the house is an acceptable place to go potty. You have to be on it, though, in the beginning, and watch them like a hawk. So that you catch them each time they are about to go, or when they have gone in the house, so you can correct them.
If not, I agree, she needs to have as little free reign when--you're not there to watch her--as possible.
You might want to hold off on getting a second one until it's under control.
Hang in there,
