That reminds me of one of my bosses that had a small dog all her life she had peed or pooped on cement never been on grass. When they first took over the property I worked at there was a patch of grass right outside there door. So the first time they put her out on it I was there. The look on her face was like " you want me to do what where? How rude!" took her forever to get used to the grass.
Sounds like you are on the right track hang in there!