Personally, I'd imagine she'd have a more forgiving accel and a better thrust factor, but not be that much faster than Knuckles or Tails. However, I haven't played as her in SA2B so I'm only basing this over the general impression given off by the character. Though increasing the acceleration is probably one of the most effective way of giving the impression of a faster character in SRB2 without actually making it go Sonic's speed.