Blaming religion is easy, but I think that would probably be a confusion of cause and effect.
Christian texts span multiple centuries, cultures, and authors. Countless stories with countless different lessons, some of them contradictory. You can find support for pretty much anything you want in the Bible if you really want to dig for it.
Most Christians don't use their faith as a justification to shun the real child they have for not being the imaginary child they wanted, especially to the point of taking their own life. I have very little sympathy for those who do.
Religion is a tool. Just as a hammer can be used to build a house or to smash in another person's skull, faith can be used as an inspiration to build a better world or to justify whatever bigotry rests in your own heart. I have very little doubt that those who preach hate against others would continue to do so even without religious justification; they'd find some other reason.
The mother is a profoundly selfish person no matter how you try to explain it.
I mean blaming religion isn't really "easy" though, and I agree it'd be inappropriate to try to say it's 100% religions fault.
But the fact is one cannot disconnect the hugely negative impact religion has on so many individuals. Representatives of various faiths constantly attempt to legislate hateful laws into existence, politicians and community leaders and terrorists of every stripe use religion as a justification for their hateful shit.
And the truth is,
because of how much abhorrent content is within these books, they are not actually wrong to interpret it this way. That is a real problem. The fight between literalism and the non-literalistic interpretation has been waging for ages, but even within these categories there are subcategories of interpretation. Truth is when you have holy books that endorse stoning homosexuals or killing infidels or raping children or beating slaves, it is obviously going to have a degenerative moral impact on a person who has been indoctrinated from birth to believe these works are the inerrant work of Godly inspiration. It does a big disservice to how serious this issue can be to merely interpret it as people inappropriately using the Bible - to use that as an example - as a bludgeon to promote their hate.
You say "Most Christians don't use their faith as a justification to shun the real child they have for not being the imaginary child they wanted", but that's not true. For example, the
vast majority of religious folk polled support the hateful legislation against gay marriage. People who attend church regularly were
76% against the law. That is in of itself hateful and using religion as a way to limit and insult the people for being born the way they were. Even though views are rapidly changing and improving every year, a whopping 46% of the country believes being gay/lesbian is morally reprehensible in the latest nationwide poll that was conducted about it. Of that number, those most motivated to believe that were almost uniformly religious - protestants and mormons and other such faiths.
So to say 'most' Christians don't use their faith as justification to shun a child is at best only very slightly true... because while they might not outwardly reject their kid in overt forms of hate, they may indeed reject everything they stand for and comment about how negative they feel that behavior is. And this is tantamount to rejecting the individual. It is hate by any other name. It drives people to suicide, the links have been shown in statistical studies.
The mother may indeed be Selfish (I think it's likely), but in a society that fails to adequately educate its people on the truth about LGBTQ individuals (and
especially on the subject of transgender folk, there's almost no education to be named of), the ignorance that can fill the void is often "closed" by using Biblical inspiration to come to their conclusions. Religion is undoubtedly a vessel for this hate. That it can also be a vessel for good in other ways is also true, but it is impossible to understate just how significant a role it plays in the negative perceptions society has of it.
Pre-Christian societies that had no significant faiths with a stated prohibition on types of sexuality were frequently much more open and accepting about homosexual relationships, for example. Some advocated it, some even engrained it into the very basic cultural and social norms the society was used to. What changed? One major change was that different faiths had different interpretations of what was acceptable, right down from traditional sexuality to LGBTQ individuals. Even traditional sexuality originally suffered mightily underneath the prude St. Paul interpretation of celibacy/asceticism.
There have been countless historical investigations showing the correlation. So even your feeling about people just preaching hate without the religious "tool" would suggest leaning false based on historical precedent. People prior did not simply replace the empty void of Biblical/Qu'ran truth with more hatred against homosexuality, at least not a significant portion of the time.