"While it is true that some of Abass' remains may have been mixed with those of the U.S. airmen with whom he died... While also true that Abass' ashes will share a single coffin with those of the four Americans..."
I agree with you.
There was no way to separate his remains from those of the others. Therefor it is necessary that he be buried with the others, therefor her complaint is misdirected. Her complaint about the other 59 would also need to be judged on a case by case basis, and probably were.
Since she got this one wrong, I'd be hesitant to take her word for the others unless she did a little legwork to find out who the others were and why they are where they are.
On top of that, he was an allied soldier fighting alongside American troops in pursuit of the same goal. Those little pieces of American soil scattered throughout Europe have a number of foreign nationals interred in them, too.
I doubt the rest of the Arlington residents will mind.