My wife downloaded a free slot machine app. But when she tried to play another app pop up and a word buy. She taught it was free. My wife is new in world of Ipad. Can I get a refund for the $49.99

My wife just purchased a free slot machine app from Shark Play Ltd. But when she tried to play another app pop up "Vault Coin" with the word buy. She is new to the world of Ipad and Itunes Store. She thought all the while it is still free because the main app is free so she click buy. This morning my daughter told her that there is a charged on her credit card (My Daughter Credit Card is used on my account) for $49.99. How can i request for a refund? Thanks