How to cage train my 7 year old shih tzu?

Since she was in a puppy mill, she was probably used to using the bathroom in her cage, and since she spent four years inside her cage it will probably be difficult to train her to not poop inside the cage. Difficult, but not impossible. Do you take your dog outside often? After she poops outside, do you encourage her by giving her treats and affection? You can immediately tell her no in an angry tone right when you caught the naughty act in the cage and quickly take her outside to use the bathroom. Then after potty time, praise her for doing the right thing. It won't happen in an instant, but through much repetition and patience, I'm sure it will change her mind before she use her cage as an oval office.