design notes:
-gay pride horse
-"armpit feathers" are usually shaved off since they're considered unsightly to pegasi, rainbow gives no shits
-on the other hand, ankle feathers are considered VERY impressive, since the great pegasi hermes, one of the fastest and most legendary pegasi there is, had wings there, and ankle feathers are considered to be shown only on descendants of hermes and on the fastest pegasi in the land.
-she's got some chest and shoulder feathers too. no opinions about those.
-just a little stocky for a pegasus! they have hollow bones and slender shapes, not as small and dainty as unicorns and not as chunky as earth ponies, pegasi strike a nice middle ground. rd is surprisingly not shaped like your typical wonderbolt, but she manages to be one of the best fliers regardless.
-she does have a jacket that she wears but i didn't want to draw a jacket on her, especially not while she's rearing up sdjf what do you think i am, competent?
-rainbow power didn't affect her permanently in any way since she's already as rainbow as she can be.

rainbow dash! always scraped up in her youth because of an inability to brake and turn quickly. those big wings are good for speed but not precision, which dampened her chances of making it in the wonderbolts, who are all about complex flight drills and maneuvers. as she got older, she learned how make up for this and eventually getting around this flaw in her flying. she's very self assured and confident, and will lift up her friends with praise, keeping them confident in their abilities too. her destiny isn't just "fly fast" like most ponies think - it was achieved when she did her sonic rainboom, but that wasn't really what her destiny is about. it wasn't about the feat of athleticism, but what it did for others. rainbow dash's destiny is to spread assurance and self-esteem to other ponies, just like she did when her rainboom helped her future friends find their destinies.