Hi there
Well, I can see your problem. If your not telling her NO firmly and then showing her where she needs to go??? How is she suppose to know not to poop in the house? You dont have to yell at her, but you do need to be firm with her during the training process... Or else, she's gonna take it as she can do as she pleases. She's hiding her poops because she knows shes suppose to go outside
They are very smart, and with another dog in the home to lead by example...she's definately aware of where she needs to go. You have to be dominant or she will
Hope this helps