Sasuke was the one to first view them as a team. Even though he called her annoying he rushed to her aid in the first sign of danger. Sasuke was a pretty awesome guy in early part one. :|
As Team 7 bonded Sakura got to see more sides of Sasuke. It wasn't just that Sasuke was cool otherwise she would have woken up when Sasuke was panicking about Orochimaru.
Anyway her love most likely blossomed after a desire to help Sasuke once she saw the darkness in him.
The problem is that this is still just YOUR subjective conclusion.
Whereas Sakura in the MANGA says nothing on this topic.
I'm not asking what MIGHT have been her reasons - I want to hear it from HER.
Again, the thing is that the shy Hinata happens to be very vocal about HER reasons, yet the much less inhibited Sakura sums it up as "not having ANY reasons" whatsoever.
I know I'm repeating myself, sorry, but I'm just trying to explain why Sakura's love seems kinda stupid as a FACT (not due to the reasons themselves, but actually to due to the LACK of those reasons to begin with).
By the way, this is EXACTLY the same reason I'm opposing NaruSaku so much as well - cause Naruto ALSO doesn't voice his reasons to "love" Sakura beyond her wanting SASUKE's attention back then in the very beginning.
It's pretty much the same, except Sakura is even more blunt about her love, while Naruto is just silent about his reasons (IF ANY).
Which is why the movie's "retcon excuse" (about Naruto mere competing with Sasuke over Sakura's attention or so) does NOT sound too far-fetched, given how Naruto gives NO info to counter it in-canon.
In fact, Hinata's love is the only one of them that HAS valid reasons behind it.
Well, even better, ya know.