Okay, the things I liked: Your grammar is excellent, your writing style is easy to follow and your formatting is good. I'm happy to see this won't be focused soley on romance and the pacing is nice. Nice introduction to Dakota.
Things you should work on: This doesn't fit in the Outsiders time period. The description of greaser girls' clothing sounds like the 80s. Not even greaser girls wore leather pants in the 60s.
The prices are inflated for the 60s. It may cost $3,000 for asthma treatments today, but in the 60s it would have cost a fifth of that, most likely.
Either labeling this an AU or setting it in modern times should take care of these problems. Or you could research these things.
And finally: Dakota is close to being a Mary Sue. I will buy that, if the Curtises had a sister, she would be beautiful and athletic, because the Curtises are beautiful and athletic. I'll even buy that she's an Olympic-class talent. But all of that, and she has fragile health (does this interfere with her athletism?) and she's a custom-bike builder (something that girls wouldn't normally be part of in the 60s) and she drag races (again, not a big girl thing -- gender roles were much more rigid in the 60s) and she becomes a master mechanic in a few weeks? Not believable.
I'd advise you to pare it down some, maybe drop the swimming and drag racing in favor of the bike building, since you seem to be very enthusastic about it. And, please, don't have her master the mechanical skills in such a short time frame. With three brothers and a bunch of boys for friends, there's no reason she couldn't have been hanging out and watching them for years.
You are a good writer and I hope that you consider and continue.