Dog Pees in House When Separated from Owner?

I have a 5 year old yellow Lab. I got her about 2 months ago. She was a kennel dog and was never in a house and was never a family dog. She is a sweet heart and does awesome with everyone. She doesn't have a mean bone in her body.

Here's where the problem comes in. When left alone all day she is fine, doesn't pee or poop in the house. She goes all night without going in the house. If I am inside she is at my side no more then 3 feet away. When I give my son a bath there isn't enough room in my bathroom for all 3 of us, so I have to shut the door and lock her out. Well that's when she pees on the floor. If I am home and shut her out she pees on the floor even if there are other people in the house. Please help.

By Andrew