This follows my own headcano. Enjoy! ^^
 
Aria doesn’t always show or say it, but he absolutely loves her daughter. After losing her old gem during the Battle of the Bands, Aria and her sisters lost an essential part of themselves.
 
For Aria that was replaced with her love for Trixie, and soon after her daughter. After much talk and shows of reformation Princess Twilight allowed, and even helped, the Dazzlings to perform a very important ritual to regain their gems called the Siren Ascension. This gave the sirens back their powers, albeit very weak and limited.
 
Now, with her reformed gem Aria guides Harmony Blitz in the hymn of oneness. A song sacred to sirens when a young siren comes of age to perform the Siren Ascension and makes their own gem.
 
For Aria it is one of the proudest moments in her life to see her daughter perform said rite. And for Harmony it was a truly amazing experience. Both mother and daughter grew a special bond on that day, and would only grow from there on out.
 
Greecian style clothing because, well sirens from Greek mythology. Also a shout out to mustlovefrogs for helping me to come up with my oc cutie.