She probably reincarnated as well. I just don't know how did she understood beforehand that he's the one. Probably Long before revelation... Some sort of gut feeling probably, because she somehow feeling his pain and regretFai x Lischen, I wouldn't mind shipping them.
But damn, Tiara is still alive for some reason... How...? I don't like spoilers so...
She wants him to find his own reason to live, not stick to ghosts (even if it's a living ghost) from his previous world for the reason. Sure, he would be happy, but it would also mean he would most likely stop looking for a personal reason to live. He never really had one, he only had a reason to die. Even now, after much development, he's still stuck at trying to make sure others can live happily, never mind his own happiness, which is still unknown for him.Yeah... this sudden revelation makes no sense... especially about the reason to live. If she told him about herself, he would be happy and feeling alive.