Remember, some of those young women may have attended public schools that didn't even say the pledge of allegiance. They may have no idea how to act during the playing of the Anthem. After all, there are many Americans who think the last two words of the song are "Play Ball"!
§ 301. National anthem
(a) Designation.— The composition consisting of the words and music known as the Star-Spangled Banner is the national anthem.
(b) Conduct During Playing.— During a rendition of the national anthem—
(1) when the flag is displayed—
(A) all present except those in uniform should stand at attention facing the flag with the right hand over the heart;
(B) men not in uniform should remove their headdress with their right hand and hold the headdress at the left shoulder, the hand being over the heart; and
(C) individuals in uniform should give the military salute at the first note of the anthem and maintain that position until the last note; and
(2) when the flag is not displayed, all present should face toward the music and act in the same manner they would if the flag were displayed.
http://www.law.cornell.edu/uscode/html/uscode36/usc_sec_36_00000301——000-.html