Issue with Turkish Airlines' Flight Booking and Unaccompanied Minor Policy

On 15.01.2024, I purchased 3 tickets from THY for flight TK2260 departing at 09:30 from IST to EDO for my daughters and their friend (ages 15, 13, and 10). Their 15-year-old friend was considered an adult according to the website, so I bought 2 adult and 1 child ticket. The girls were dropped off at the airport by their mother, who left after they checked in their luggage. When they were about to board, they were told that my 10-year-old daughter could not board without an escort and that a form needed to be filled out by her mother. Although their mother returned, she couldn't make it in time, and my daughter missed the flight. There were no warnings on the website or at the check-in counter. At the last moment, they refused to let her board, which I believe was based on their discretion. How can you consider someone over 12 an adult but require an escort for a 10-year-old? This policy is absolutely nonsensical. I am requesting a full refund for my ticket.