I didn’t read it that way either, but WOW, that would explain a lot of things! A very good friend of mine from a very conservative religion has a child who came out to her while in HS, but only after trying twice to kill themselves and had packed before telling the parents, expecting to be thrown out of the house. Their schooling took a hit in terms of achievement, not surprisingly, as they struggled with their identity. Luckily, my friend and her H decided their child meant more to them than anything else and accepted them completely.
If the D in this story believes she is going to hell for being gay and that nothing matters, it would fit with everything the OP is saying. In THAT case, I would direct both mom and D to the “It Gets Better Project” for encouragement and to search for a good therapist that is gay friendly. I don’t know how hard that would be in Ireland, though. The country may have just voted for gay marriage but it’s still a very conservative place according to a friend who lives there.