Hello dear and welcome to the medhelp forum. Popping sound in the head could be related to Eustachian tube dysfunction. This tube connects the back of nose to the middle ear and aims to maintain the ambient pressure inside the middle ear cavity. I hope your daughter is not suffering from an upper respiratory tract infection. This could cause Eustachian tube blockade and sensations of popping or clicking along with ear pain. This may progress to middle ear infection. Consult an otolaryngologist for evaluation. Does she complain of any neck stiffness or pain? A CT scan neck would be required to check any vertebral trauma. Wishing her all the best.
The first things that come to mind is either a joint in her neck is a little rough, and that will cause more of a cracking sound, or her ears may have a problem that causes the ears to pop, like happens when either too much earwax is in there or when you're in an airplane and altitude changes make them pop.