It says nothing of 17 in relation.
edit: Hmm. Ya know what? I kind of glanced over the fights again and nothing stands out about 18 in particular. She's never separated from 17 either, though. Apart from when she hit Shimishimi and 17 hit Seven-Three, they both were in total sync, and nobody separated them power-wise (more like the opposite). I mean, am I supposed to believe that just being 17's twin and attacking together makes up for the cataclysmic gulf in power between the early Cell arc and the Tournament of Power? Seems odd to me if Toyotaro still intended 18 to be unchanged in strength, yet even keeping up with 17's speed, let alone reacting to Moro.