I'd be pretty peeved.

It's not like your daughter is going to drink a case of Moet! Especially if she is a Skywards Gold herself - she absolutely has earned the right to the benefits.

I reckon my 9-year old son would wave his arms if this happened to him.

I'd be asking them "at what point do you consider my child an adult?"

You're not missing anything at all. Write to EK in your home base and express your disappointment with the policy (not the incident itself).