The emo teenager and the rowdy kid.
 
Flurry and starburst might have met as kids. But Flurry was never really fond of the diaper wearing brat. And Starburst could not yet form cohesive sentences. Due to the long travel distance between them, they never saw each other too often, and did not mind each other too much when they did. Flurry was too bussy being fauned over by everyone, even when there was another baby in the room. And starburst was too young to care about that prissy princess. But when they both hit their rebellious ages, someting between them just clicked.
 
 
If I were to put an aproximate age on the girls, I would say that Starburst is the equivalent of a 10 year old while Flurry is roughly 13.  
three years might not sound like a lot. But for a kid - Even one year is an eternity. and three is the difference between middle school and upper school.
 
Despite this. the two whent along like peanut butter and yelly. A lot of other teenagers would not have wondered who this little upstart brat was. And Flurry did too. She had a way of keeping other at a distance.  
See - Flurry never had many real friends. Those that were forced on her were usually intimidated by her. Her massive wings and unusual height gave her an intimidating aura that made others cower before her.
 
But not this little brat.
 
Its a usual show of Pegasi prowes to flex ones wings when trying to impress the opposition, or to try and appear bigger when threatened. Its an old bird brain instinct. “look at how big and tough I am”.
 
You could cut the tension with a knife as the two rebbels stared each other down. Taking each other in, messuting each other with their eyes. Flurry usually “winns” at any first impressions by being casually the more dominant presence in the room. But this little brat did not give a flying feather-fart about authority. Flurrys dominating precence was met with Starburst “come at me bro” attitude.  
That helped build the bridge between them. As for once, somepony did not look up at Flurry. Despite literally bending their neck looking upwards, somepony did not see her as a superior.And over time the two became each others best friends.
 
Another thing that the two have in comon is their height problem, though from oposite sides. Starbursts is upset that she is too short, and nopony takes her seriously, since she looks younger than she is. Flurry is upset that she is already bigger then everyone else, and is worried that she has not stopped growing.
 
Both wear baggy clothes to conceal their physicality - Starburst to hide her bony frame and appear bigger. Flurry to hide the fact that puberty is hitting her like a runaway freight-train. And she conceals her natural beauty behind tons of make up and raggy skirts, so that people won’t stare after her in the streets.