I didn’t either.
But as the tech support guy I have to know things.
It’s actually quite rare to have Lily under 4 hearts.
Since you need her at 3 to buy the bar and you have to buy the bar to progress main story.
But after buying the bar, if you never talked to her again the 4th heart event never happens.
And Arc did the cutoff at 4 hearts or not. I kinda disagree with the cutoff being so harsh, but eh. What can you do?