With Four's head coming along I focused my attention on her teeth today. Using the techniques Alan suggested I have what feels like a more realistic jawline.
I think there is still room for improvement, there's quite a bit of geometry cleanup required for one, but this feels like a significant improvement over the previous more simplistic model. The rearmost teeth could do with some raising perhaps, but so far I feel the process is much stronger.
Four is an insectivore. In part of the story she eats smaller insects and her body is thought to contain a compound likened to spider-silk. So her teeth need to be optimised to pierce or crush hard carapace (on recollection giving her a nutcracker-like set might sell that she can eat insects. But as an upper-level predator she needs to be adaptive and teeth designed to crush hard carapace won't work so well when trying to pierce skin. So like a number of carnivores, she'd have more than one type of tooth in her mouth, each with different functions.
That may require retraced steps but the crafting of the gum sockets was probably the most taxing part of today's build. That might not need too much changing if I'm going to be swapping teeth out.
As well as that I've tried using Maya gemoetry to sculpt some of her muscle. I've only done her collar and front leg (which doubles as an arm) so far and might need to do a little work on the shoulder to sell the structure a little more, but it's progress. I'll look into refreshing my memory on building quadruped limbs and body at some point, the thumbnails for the tutorials (where the subject is a horse) suggest they could include tips for sculpting particular muscles.