Konzert unter 16?

she will be at night from the concert to the next day 18

What now? Has it on event day (20.11.) Birthday or the day after? If on the day of the event, it is already 18 on the day and can also be an education officer. But if only one day later, it is only 17 on the day of the event and therefore cannot be an educational officer.

Since you are only 15, according to the rules of the organizer, you need an educational officer with a Muttizettel or a person entitled to care (a parent).

This is what the organizer writes in his AGB:

2.2.2. The organiser does not enter into a contract for a child up to the age of 7. Children and adolescents aged 8 to 15 years of age only have access to the event accompanied by a person entitled to care or a person entitled to education. An educational officer shall be a person over 18 years of age, in so far as he performs educational duties on a permanent or temporary basis on the basis of an agreement with the person entitled to care for persons or to the extent that he or she assists a child or a young person in the course of training or youth assistance. Parental Officers shall provide a written proof of their assignment and, upon request, provide a copy of the identity card of the person entitled to care. From 16 years onwards, admission to concerts is allowed.

https://markusgardian.de/agb/