I think because they think she traded their religion for someone else's religion and feel betrayed for their religion what they believe in in their country. Perhaps also with all the terrorism label on them they feel like well why you want to go to their religion if Americans are putting this label on us and you'd rather believe in their beliefs. Even though America is not the only place where Christians are you understand. Like Muslims are usually Saudi Arabian, Arabic etc. To sum it up because this was kind of hard for me to answer because I had to think about it basically they feel that she betrayed their religion beliefs. My opinion. Hope I answered your question :)
its not like that with EVERY muslim....im a muslim, and if i have children some day, ill never beat them if they become christians,,,,,i will only became depressed if them became women that wear miniskirts, or something like that, you know, inmodest things.....cause if my girl says me that she has a boyfriend adn wears tiny clothes, i'll tell her, well, you are welcome in my house, but if you want to wear those things go to a table dance...