I think this redesign fits my idea of Rainbow Dash much better than my previous design, so here it is!
 
Rainbow Dash, older than only Pinkie and Twilight and only taller than Pinkie, is a short and athletically-built mare. Her wings are short but well-proportioned to her body, making her built for speed above all else, which is opposite to the long-winged Fluttershy who is better meant for endurance and gliding than speed.
 
Born from a fairly long line of pegasi and only having extended family members who are earth ponies or unicorns, Rainbow Dash’s genes set her up as an excellent pegasi specimen. Her markings, from her lighter breast feathers to her tail feathers, are standard for the majority of winged ponies. Dash’s body is meant to be as aerodynamically fit as possible, which shows from her layers of soft cyan feathers and her inability to grow furry fetlocks like her friends. As an athlete, she prefers to have her hair short and out of the way. Looks don’t matter to her as much as convenience does, and she rather enjoys the short hair that can never get in her face.
 
If she’s not working as a Wonderbolt Aerial Performer (and later the Wonderbolts Captain), Rainbow Dash enjoys visiting the Ponyville Crystal Palace to read adventure stories to foals or going to the Ponyville Spa for a massage, hoof maintenance, and a nice relaxing session in the sauna.
 
Thunderlane, of all ponies, caught her eye shortly after she became a full-fledged Wonderbolt. The two enjoyed similar things like camping, being competitive fliers, having “secret” hobbies outside of flying, and their pets. The moment Rainbow Dash saw that her tortoise Tank enjoyed Thunderlane and all his coddling, she was set to go. After all, Tank was even more picky than she was when it came to mares and stallions that she brought home. More than a few romantic interests had been snapped at by her pet, which would deter them from coming back to her house. So the moment Tank not only got along with Thunderlane, but also his cat Shaggy, Rainbow Dash knew he was something special.