The 'Uses Gravity to Give Impressions of Super-Strength' thing is a fun effect, though it could 'Affects Others' if other characters have been shown moving stuff that she moved. I like the notion of 'taking a weird power and running with it'- it shows more cleverness than the usual American comic book thing of 'give them a standard-issue power, or the Full Strength Package'. Yeah, this seems like a great case for 'Best Girl'- not too feminine to freak out the little boys reading, not too fanservicey to turn girls off the character (or be the puerile 'Fap Bait' one- a usually-common role in shonen), and she seems like a nice, friendly character from what you've said here.
