She has a point, it's definitely appropriation, not so sure about the cultural part since it's just an icon and not being used to define a specific cultural aspect.
That said, as an anthropologist she should be perfectly aware that nearly every society in the history of the earth has appropriated something from previous cultures, it's called building on the past and has led to the continued growth and improvement of society in general.
So, the big question for her should be - what's your point? Yes, it's appropriation, darn near everything is, live with it and grow. Or immediately stop using anything that has been appropriated from a prior civilization, including the house you live in because it was appropriated from cavemen who decided it would be better to sleep inside vs getting rained on every night.
I like my Thunderbirds so I'll continue to buy and play them. Likewise I like the strings and the frets and the tuning keys and bridges on them, which were all appropriated from prior civilizations that developed stringed instruments. HMMV