nervous neck cracking

My 10 year old daughter recently developed a strage habit. She lifts her shoulders and throws her head back to, she says, crack her neck. She seems to do it about every 10-15 minutes. Not sure if it is body or mind related. Her mother and I went through a divorce 3 years ago, she has gained some weight and having trouble paying attention at school, but grades still good. Could be stress/anxiety? problems at home with mother? maybe her backpack is too heavy on her shoulder? Her mom seems to play it down and we will get to a doctor soon, but any thoughts anyone?
worried father