I agree that you should have her checked for a UTI - especially where she is drinking a lot on top of the peeing.
If there isn't anything medically wrong after you have her checked, could it maybe be that she just isn't emptying out all the way when she goes. I know when my pup was little, she would be so excited to play with the big dogs or get distracted by noises in the woods that she would squat, go, but stop mid stream. I thought she had finished, but she'd come inside and go. Once I watched her more closely, I could tell that she was doing that and would stay out longer and sure enough she would go again. Once she went the 2nd time, I knew it was safe to bring her in.