Apple Music Family Sharing Trial

Hello,

Back in 2015 I signed up for an individual 1-month trial of Apple Music. Currently, my family has family sharing for our Apple ids. Today, my wife subscribed for the 3-month family trial of Apple Music. I received the invitation to join the family and then I received an email that we were charged $14.99. Why would this happen if she nor did the rest of my family ever use their free trial?