No need to evade the truth, to put it plainly if it was a Muslim girl then she would be ostracized or severely reprimanded.
*******************************************************************************
Culture blamers this is for you: (Note I've written in simple terms. It's far more complex than this.)
And for people in the comment section who believe that this is only true for Muslim girls of Asian decent (i.e. Pakistani, Indian) , they're wrong. Whilst it is stereo-typically true that Pakistanis and Indians (regardless of faith) are obsessed with reputation and shame (seen by uncountable acid attacks, honor killings of close family members, expulsion of family members etc.) the harsh actions towards a Muslim girl found guilty of this sin cannot be fully blamed on culture . Look at other ethnic groups (Arabs, Africans), where some of whom magically happen to be Muslim and act similarly to these Pakistanis and Indians. But wait! That could also be due to culture too! Oh yes and while we're at it I'm sure we could find a dozen pieces of evidence of how it relates all to culture and not the flawless Muslim community! Evidence points all too strongly to a trend that Muslims of most culture tend to act more severely with a girl if she was to do such an action (than with the opposite gender i.e male for those who do not know). The point I'm making is it is about time the Muslim community can accept some blame for their actions, and improve from there on instead of talking of culture to be some sort of belief system that is dissociated with religion and its interpretation.
The root of the problem is far more complex and inevitability would be in order to evoke change or to keep the status quo.
***************************************************************************************
Extra: logical explanations as to why it is so and conclusions from these
One possible reason why she is dealt with more harshly is due to the fact that it is only permissible for Muslim men to 'marry people of the book' hence see it as a more of a sin on the woman.
According to most scholars, men lead the marriage under Sharia. Thus a logical explanation is that the father could have more control over his children's faith than the Jewish/Christian wife. So what you see is that compared to women, a higher proportion of Muslim men marry.
But even marrying People of the Book is not recommended for men (since it's exclusive to them). Why? Incompatibility. The wife would have to be very pious to Christian standards, i.e following the bible intensely in the respect of prayers and daily life for her Judeo-Christian values to be 'more in sync' with that of the Muslim man. The bible ordains for wives to be submissive to their husbands. If this were the case for marriage this would bode well with the husband's demand of the children going to mosque, practicing Islam.
But then again take a look at reality. The logical argument above is purely conceptual. IN REALITY, Muslim men who marry Christians, Jews mostly end up with kids who are non-practicing, whilst their marriage is deemed 'okay' by some of the Muslim community.This is odd. Surely it could be a sin on the father for not having his children practice his faith.
Perhaps the 'conservative' Muslim community ought to tighten their rules of marriage for men in order to prevent them from sin, since they have done so for females.