Daisy is pretty well known now and people still like her so I don't know if the non-conformist thing holds water. They would have moved on to different character. I used to pick Daisy because she was like the kid who always got picked last in gym class. As silly as this sounds, I kind of felt bad that no one ever picked her.
I used to pick Peach for no other reason than she was the best character from Super Mario Bros. 2 which didn't matter in Mario Kart, but whatever! I grew tired of Peach because she's portrayed so inconsistently. Some games she's kicking ass then the next she's helpless and annoying. Daisy kind of came back at the right time. Her near clean slate let me fill in the blanks of her character. I tend to imagine Daisy as the BAMF version of Peach who hover jumps, throws Psych-Bombs, and bashes people with her crown... except all the time. And if you compare personalities, it's no contest. Daisy wins. That said, it'll break my heart a little if she needs to be rescued in Super Mario 3D World.
Also, Daisy's "Aw, brutal!" from Mario Kart Double Dash is the second best sound clip of in the Mario Kart series. Only Mario's getting attacked yelp from Mario Kart DS is better.