Potty training

Did Layla poop on the pad previously? A lot of dogs will not necessarily do both pee and poop on the same pad. A lot of owners have to let them pee on the pad and take them out if possible when they have to poop. Some dogs have a schedule when they usually poop. Morning and evening. Was she kept in a confined area to learn to go on the pad?

I'm sorry to hear that your yorkie is regressing but yorkies are not use to change. They like things to stay the same from the first day in there new home.
Yorkies are very stubborn and difficult to potty train if you don't stay on top of the situation...here are some things that you can do...lay down a potty pad, when you know they have to go potty talk to your yorkie so that he/she knows that that's were you want then to go potty/poop and if they leave the potty pad, continue to put him/her back on the potty pad. After they potty/poop on the potty pad, praise them or treat him/her right after it happens. Leave that potty pad there with the smell of potty/poop (just pick the poop up or lay a paper towel on top of it so the smell is still there) on it so that they know that that's where there suppose to potty/poop until they get the hint. If you don't want to use the potty pad then the bell system works great. Get a little bell and ring it when your taking your yorkie outside to potty/poop and when they take care of there business ring the bell and praise or treat them. Back inside the house allow your yorkie to play with the bell so they get use to the idea of ringing the bell when they need to go outside to potty/poop. But when the get the hang of things, put the bell next to the door so that they can ring it to let you know when they need to go outside to take care of there business.