Maybe she is not drinking enough throughout the day... try to make sure she gets drink breaks during the day by placing her in front of the bowl and dipping your finger in it to entice her to drink. I would think if she drank more during the day she would sleep through the night.... But, I do have a 13 year old who gets up every night at 2 AM for a drink... I may try my own advice!
Or you can add some water to her food...