Force Quit D - Where is the hint?

[GistOfSpirit]

I've finished the game several times, so I'm not asking what the hint is.

I know that the answer is "brooch" and "blue bird" but although we know from VLR and ZTD that the brooch was given to Phy by her mother, I can't remember Diana ever saying that she got the bird from hers.
I got it by just guessing from the shapes, but what is the proper way to do it? Does Diana ever say that?

[GistOfSpirit]

I just realised.
It said "a mother's mementos". I thought it meant mementos from two mothers for some reason, but no, it's the same one (Diana).

[Miko]

It is in the timeline where Diana and Sigma have Phi and Delta in the bomb shelter. Diana and Sigma teleported to a timeline where they have already died. Only Akane escapes, leaving Diana and Sigma trapped in the bomb shelter, dead to the world. At this point it goes through multiple cutscenes of their interactions leading up to Phi and Delta's birth. They are in the room with the changing walls when they have a discussion about Diana's blue bird music box.

[Miko]

Also fun fact, "music box" also fits in force quit D. You can either use "music box" or "blue bird." Outcomes are the same.