Of course you know many people find it disrespectful. I don't. But I don't see the flag as ONLY a symbol of American military, but as a symbol of America as a whole (including the military).
The fact that the protesters know if will be offensive and controversial is the ENTIRE reason why it's done during the national anthem. If it was done in the locker room behind closed doors, nobody would pay attention. Of course, you know this and your daughter knows this, as that's the point of even doing it. She is doing something that will purposefully antagonize others who share a different value system in order to bring attention to a value that is dear to her heart. That's fine by me, but don't pretend it isn't controversial or that she doesn't know it will offend a sizeable chunk of reasonable people who think there is a better venue to display her viewpoints.
Also please don't pretend that her display of protest makes her immune to criticism for her decision. That's part of the price to be paid for raising her "voice" in such a controversial manner. f you don't realize that or if you didn't see that coming, you should be advising her more wisely, go find an echo chamber that will tell you how awesome you are, or else get some thicker skin.
As far as my value system goes, big thumbs up to the kneelers. It takes bravery, and I hope their message gets through.