I need help with this too. I just rescued a two-year-old Boston Terrier who seems afraid to poop outside. He waits until he comes in but also he waits until no one is looking. He hasn't gone in over 24 hours cause we've been watching him and taking him outside. Does anybody know why a dog would be afraid to go poop outside?

Poor puppy! Have you tried walking her until she has no choice but to go? It seems eventually she would not be able to hold it any longer, and then you could give her tons of praise, goodies, etc. Our Chihuahua likes to walk for awhile and find the "perfect" spot.
Or maybe you could try this- if she has gone in the house, quickly clean it up, but rather than disposing of it as usual, take it outside, and put it right where you WANT her to go, and every time you take her out to go, take her right to that spot, and praise her extensively once she does it in that area. Hopefully it won't take long.