My rescue dog wont go potty outside!!?

We rescued a schnauzer from a puppy mill months ago and are having a huge problem potty training her. We have her on a regular feeding/ taking her out to go schedule, but she WILL NOT poop outside. I always take her out about an hour after she has eaten and right before we need to crate her. After I put her in her crate and leave for any length of time she will go in her crate. I have taken her out sometimes 18 times a day and she hasnt gone, but I bring her back in and turn my back for 5 minutes and she has gone. I have used a crate and even tried blocking her in the kitchen, but neither work. We have tried using a short leash, long leash, and even just letting her wander around the yard...nothing! I am so tired of giving her a bath or mopping the floor every time we come home. OH, yeah, and we have even just taken her with us so we didnt have that issue and she has gone in the car!! Please help my sanity!