Our Phoebe is a 17 year old cocker that until last week, never had problems going outside. But a week ago we had our patio enclosed which means she now has a second doggie door to go through. No matter what we do (have tried treats ad nausium), she doesn't like going outside to do her business. She will early in the morning and late at night but only after lots of coaxing and lots of treats. I realize that the outer doggie door flap is black and she's not used to that so we put white paper on it but that still doesn't work. Help! Any suggestions?