As long as we're dealing with the letter of the law and not the spirit, i.e., claiming that a 12 year old who hangs themselves (where'd she learn to do that? Was that particularly Christian or a Christian suicide?) can be said to have committed suicide for religious reasons thanks to a note that attributes her death to a wish to be reunited with a loved one in heaven, we might as well throw that line of reasoning out the window too. Her note said nothing about heaven:
"Maria, from Leszno in Poland, had left a short note, which read: 'Dear Mum. Please don't be sad. I just miss daddy so much, I want to see him again.'"
Source
Now most people would say that believing you are going to see deceased people again is a religious idea. But Poland isn't known for it's religious people, there are multiple religions with ideas about death, and there are people who aren't religious who believe in life after death or tell their kids this. To my knowledge, no religion teaches children how to hang themselves.
So, we have a 12 year old girl who knows about a form of suicide girls especially and children in general do not commit who, as a reason, simply says the wants to see her father again. We can't even say it was a religious teaching that gave her this idea (one can see it in movies, on tv, in fairy tales, in mythologies, etc.). It certainly isn't necessarily a Christian idea and there is no evidence she was even actually taught this rather than picked it up and interpreted it which, given the fact that the religions which tend to have adherents who believe one can be reunited with the dead are also religions which have doctrinal reasons against suicide, is probably more likely than that she was taught it.
Moreover, if we follow the underlying logic of "ideas that can be harmful to Children because of the possibility of suicide" then most religions (especially those more influential and/or prevalent in the West-Christianity, Judaism, & Islam) are beneficial here.
There is no basis for arguing that religious teaching really informed this girl's decision as we don't know where she got the idea that one can meet deceased people, we don't know how she learned to kill herself by hanging (at 12), we don't know who or what caused her to believe that killing herself would allow her to reunite with the dead, and current psychological and medical theories hold that a child who chokes the life out of themselves at 12 has a severe medical illness (or, in more psychological terms, is severely distraught) and it is not because of religion.