I don’t know if I already said this one, but: Any time the Alicorn Amulet lies dormant for too long, it will disappear the next time it’s left unattended and reappear somewhere that will allow it to find a new host, often the very same shop that Trixie bought it from.
Since her change of heart, Diamond Tiara occasionally has classmates asking her for favors. She’ll never tell anypony, but it actually kind of makes her feel good to help. Plus, they’re usually willing to repay the favor, which is helpful on the days that she “didn’t have time to pack lunch” (read: days when her mother will not allow her to have food) and needs somepony to share with her.