Always thought Powergirl would have high fashion sense (seems to fit her personality I guess), so her costume would be the trendiest of all the other super heroes/heroines.
What I gave her:
A scarf! Super trendy (at least amongst "hipsters").
A jacket! Different than a jumpsuit.
Red! A color that "suits" her!
Heels! It's been done before, but it (kinda) actually makes (a little) sense (not really). She flies so heels don't matter, and ladies dig heels and PG is a female so... yeah heels.
Sleeveless! Show off them guns!
Shorts, made sense at the time. Athletic, now (kinda) dumb.
Haircut has major swagg
Random 3rd fact
SPLENDOR ENTERTAINMENT: A MOMENT OF GREATNESS