I'll be honest with you, this is kinda how I feel about Spitfire (kinda...because I'm kinda starting to like her as well; damn it girl, stop making me like Spitfire!). I mean, Rainbow Dash is one of the Elements of Harmony, she won the Young Flyer Competition with a Sonic Rainboom, she fucking SAVED YOUR LIFE WITH IT SPITFIRE, and plus you clearly like her, what's the problem here ?!
(Watch Spitfire have a very reasonable explanation, or watch her say she was just talking with Soarin about sending the invite to RD when Fluttershy just stormed up to them, prompting Fluttershy (and me) to respond, "Oh...I'm so, so sorry, it's just that Rainbow Dash is my friend and I want her to succeed and everything...")
All what I can think about is that Celestia put some strings to keep RainbowDash out of wonderbolt team ( she have wonderbolts in her pocket after all ) so that elements of charmony wont get separated.