I have a 6 year old female dog who is potty trained and has the ability to use a doggie door to go outside. Nothing drastic has changed in our every day lives, but she started peeing at night while in her kennel about a month ago. She is let out before bed but in the morning her bed and kennel are soaked. Why would this be happening all of a sudden. When is a dog considered 'old'? I keep reading that older dogs may have this problem.

Have you taken her to the vet? This could be a bladder infection, or another medical condition.

You first need to rule that out before anything else.