Tonks...the MAD ROCKER GIRL.

I think Tonks would have been a fair student, she'd mess around a lot and not be that great at Maths and arty things but she'd pass fairly well

She'd be in a band and be obsessed with rock, she might even play the guitar or drums, but probably wouldn't sing. She'd be the class clown and would pursue the rocker-life after school. She might work a few jobs here and there to keep the money coming but rock would be her goal.
As for the squib-ness...hmm...Tonks' life probably be very different, but she'd still be the same old Tonks. Though, I'd imagine she wouldn't believe that she's a squib and keep trying to do magic anyway

It may take away from her hyperness a little bit though, if you honestly think about it.
GREAT discussion Linda!