My situation is similar to yours. Lola is also 7 months and will occasionally sneak out of sight and have an accident in another room where we don't spend much time. I, like you, also think she does this because it has been so cold and she doesn't want to go outside (can't blame them!). I also think it may be related to regression as this is her adolescent stage. She also pretty much has free roam of the house as long as I am watching her and she sleeps in a crate at night and goes in her ex-pen when I am not home to watch her. I'd really like to teach Lola to use the potty bells, as of now she usually just stares at me by the back door when she has to go out, as if I'm a mind reader haha. I think putting a set of potty bells in your dog's ex-pen may encourage her to let you know when she needs to do her thing outside. I'm interested to read what other's have to say about this too!
Lauren & Lola