My 6 month old border collie/labrador is a troublemaker!

[Stina]

I really need some advice! This is my first time as a dog owner. My dog is a happy and curious female, and 1 one week ago I had her neutered. This is not very important though, cause since I got her, she sometimes pee inside the house. I've had her for about 4 months, and she was used to pee inside with her other siblings. It's only in the morning, when I'm asleep. Sometimes I sleep with the bedroom door closed and I let her sleep in the bedroom with me -and she doesn't pee! It's only if she has the chance to go downstairs that she'll pee. I've tried too remove the smell with products I've seen people describe on other forums, but it has had no effect. It's always on the same spot and it doesn't seem to be about marking, since it's a lot of pee. I make her pee in the garden before I go to bed, and sometimes she wakes me up and I take her out, normally early in the morning. But most of the times she sleeps through the night. I know I could just keep my bedroom door closed, but I'm just curious about her behavior Hope you guys can enlighten me!
Ps. sorry for my poor english!