Yes. Drinking less water can be the reason for that. If she doesnt have fever or any other complain then less water ibtake must be the cause.
Next Steps
still if she continues to complain about pain, get one sonography Done. also check fpr any local injury. also notice her urine color. if it is like clear water then fine, if yellow then she is drinking less water. if it is whitish then u need to do urine test again.
Health Tips
give more water, in any form such as juice also if ahe likes.