My chihuahua wont poo in the training pads or outside really?

She knows that go potty means to pee, but she doesn't know that it means poo too. She wont go outside at all. She holds it until like forever and then goes in the house. We watch her pretty closely, but she will just hold it ALL day. I say go potty and she pees on the mat. Then she walked to a corner and 5 seconds later theres a turd on the floor. Why does she do this? (She WILL NOT go outside unless she's had to go all day or you stay outside for like an hour)