I need help re-house breaking my 4 year old dog.?

Her name is Dazie and she is a labrador retriever. When we first got her as a puppy she was an outside dog. but about two years ago we brought her inside because she got heartworms. She has never used the bathroom in the house until a couple of months ago. I don't know why, she used to let me and my family know if she needed to go outside. She would get out attention someway. Its not everyday that she does it. I don't understand why this happened and how to put a stop to it. When she did it the first couple of times I scolded her and put her outside. You don't have to tell my that doesn't work because I figured that out.