Unfortunately I pretty much have no idea what a girl looks like so I've had to do some pretty intense research, deciding that people wouldn't be too happy about me going around taking pictures of their young daughters I though i'd look at some previous female cartoon characters from throughout the ages.
I learnt many things from this research, mainly that 'kim possible' is a total babe but also they all have very distinctive head shapes and eyes, usually accompanied by monster eye lashes. There seems to be two trends, either going for the whole overly cute thing like 'hello kitty' or the kind of without gender thing like 'Dora the Explorer'. I think for the purposes of my lady seen as though she's going to be kicking all the arse i should go for the deceptively harmless look. The big eyes and all that jazz, along the same lines as the powerpuff girls but more detailed and hopefully in 3D.