I would. Even if you include the number of people killed on 9/11, flying is still safer than driving. In fact, I expect it is even safer now given passengers are more than willing to crush an uprising. So the only way I would worry if I were your sister is if she is or is married to a big bury Arab.
LOL :) I sure as heck wouldn't want to even look slightly Arabic right now. I think if I did, I'd make sure to wear lots of patriotic stuff.