Is this her first few days in YOUR home? Give it time. Even though potty training went well at the breeders, you yanked her away form mom and her siblings. Its ALL new ot her. Maybe she never saw grass and stone before -- maybe grass, or stone, but not both. Its a lot for her to process. Remember too that she's young. Its not going to happen overnight, especially if she's adjusting to life with you.

If she's been with you for a while, and has had a few good weeks, then its quite possible she heard/saw something in that enclosed area to spook her. Try to figure out what might have spooked her -- it might be as simple as water splashing out of the pool onto her back.

Also, when she piddles, is it right in front of you or does she run into another room where you are not present?