Is she a spayed female? If she is, there is a common condition, can't remember the name of it, that causes them to "leak". Or if they're asleep, they will unknowingly pee in their sleep due to relaxed muscles. Your Vet can recommend options to treat this condition. Medications, Cranberry or fresh parsley mixed into their dog food and also surgery. But the main thing is making sure the dog is taken out regularly and allowed to exercise and have time to do their business outside!
Make sure you take your dog out at least 3 times a day. And don't forget to walk him or her for at least 20 minutes twice a day because sometimes all that built up energy will make them get too excited and pee. I'm talking from experience. I've had a lot of pets, and I dog-sit. If it gets too bad, you can buy puppy pads from the store or a "potty patch" works well too if you can't take your dog out too frequently