Freedom of speech doesn't require that you are right - or even that you have a valid point. But it also doesn't guarantee that those to whom you are freely speaking will all agree with you - or that they will not freely speak an opposing viewpoint. It simply allows you to enter your thoughts into the marketplace of ideas without fear of landing in jail or otherwise being penalized by the government. .
I think she was wrong to interfere with their little tantrum the way she did. Presumably, they were the ones who procured the Chinese-made cloth with the stars and stripes from the local Walmart (making a couple of assumptions here). Thus, it is their property to do with as they please.
I do, however, agree with those who point out the irony that if the symbol being trampled were a Koran, a rainbow flag or something else then they would have been implored not to do so because it might upset some people. Have we gotten to the point where people are not upset at seing the American flag trampled? If so, then the protesters may have picked the wrong symbol. If desecrating the flag elicits a collective shoulder shrug, then what is the point?