My biggest problem is that the game makes it seem like it's your fault: mechanically, there's nothing stopping you from going to the forest ahead of time. So it seems like it's your fault, but it's a forced plot point.
I don't necessarily mind that springing the truth onto her then and there isn't a good idea; in my opinion, the problem is that that's the only factor that determines whether or not she commits suicide. If this game's interactions were more open-ended, and you maybe didn't treat the elf girl super well or something, and you actually could go to the forest early and save her mother but just didn't, then I think it could be a reasonable situation: she's trapped with all these humans who aren't nice to her, and her mother just died because of one of them was neglectful, so what does she have to live for really?
But in the game as it currently exists, the MC is moving heaven and earth, doing everything he can in order to help the elf girl, even at the risk of his life. He should basically have her full trust, which is why it feels wrong for him to not be able to tell the truth. Moreover, as I said, there's nothing in the mechanics of the game that prevents the player from going to the woods early: it's just a scripted event. So the game is essentially blaming and punishing the player for something they didn't have control over, and which they could have prevented, had the game let them.
I'll try to bring these points up with the devs if the occasion ever presents itself. I'll have your back, fellow elf girl stans.