14 year old girl travelling to Spain

[Ilonushka]

Hello!
I've been flying with Ryanair lots of times and haven't had a problem until now. The situation is following. I booked tickets for the father and his daughter. They are both travelling to Barcelona. The difference is that the father is going back home in a week and his daughter is staying in Spain. For the father I booked both ends tickets, and for the daughter I booked one way ticket. They both got different reservation numbers. Now, when I am trying to check in the daughter, the system says that she is not 16. She will be 16 in a year and she will travel with her father. What should I do in this situation?
Thank you in advance