The hijab is a sign she is FIRST a Muslim. but an American secondly. . She is loyal to a country only to the extent that does not conflict with Islam. Therefore, Muslims must denounce any person, politician or country (which is in fact any western democracy) that does not uphold Islamic submission to Allah. The mayor of London believes exactly the same thing: it is impossible/forbidden to be critical of Islam, no matter how much blood is shed for Allah.
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Islam means submission. It means that you submit to the rule of Allah as written in the Koran. The shahada, the prayer oath of obedience, "There is one God. Allah is God. Muhammad is the prophet of God.” is the foundation of Islam and said of by all Muslims. One must put Islam ahead of all things, even one's own life. The shahada also is the white text on the black flag of ISIS. How could she be critical of them?