Nobody on here can cancel anything, we are fellow users and these are user forums, not iTunes Support.
What is on her card may only be : About payment card authorisation holds in the iTunes Store - Apple Support
Purchases are considered final but you could try the 'report a problem' page to contact iTunes Support and see if they will cancel it as a one-off : http://reportaproblem.apple.com
Or you can try contacting iTunes Support via : https://support.apple.com/contact or https://www.apple.com/emea/support/itunes/contact.html