It hit me when reading the birthday chapter, did Ayu's family not send her anything?! If they did than Yunari probably wouldve noticed sooner. And it didn't even look like Ayu had communicated with any of them other than her cousin then either. What a subtly sad detail (assuming I didn't miss anything).
They basically disowned her in chapter 1.
I've always wondered what they told her cousin in that phone call, since the cousin seems to think the parents will be worried, then calls them, and then announces that they are allowing her to stay.
I assume the last part is a lie and they said something along the lines of "We don't care what happens to her." But that's still weird that she would let the idea of returning Ayu to her parents go without further hassle or explanation.
I guess it's probably so that can be a revelation in a future chapter (also makes Ayu's relationship even more unexpected).