Still working out the finer details of her hair, but I'm much happier with this draft so far.
Parting farther to the side and adjusting the curve of her forehead plus the volume of her bangs seems to have helped. Tried to go with tightly parted and pinned to keep the bangs out of the way, while going for a looser and unkempt appearance everywhere else.
The wide forehead on the initial draft was somewhat intentional, but it didn't work as well with Deux's hairstyle compared to Ple's and was definitely misshapen on the earlier draft. One of the troubles with staring at something for so long is that it gets hard to tell what exactly is off, which is why I appreciate the constructive feedback you guys have been giving.
As for Shiiko, she's probably my favourite GQuacks character design, especially with the messier hair after taking off her helmet. Will give her a shot too once Nyaan and Deux are finished.