I really need some advice with the potty training. Tessa will pee on the pee pads or outside without a problem. She is , however, pooping in the house and usually somewhere out of sight. I have never yelled at her or punished her for not pooping on the pad so I don't understand why she is hiding her poops

I have been trying to train her with a bell but she usually just follows my older dog outside. I lavish praise on her when she does go outside and she gets a treat. I just don't understand the pooping thing?