Creating additional character models is a huge amount of work (lots more art than you expect, modeling/movement, etc). The dev team had previously mentioned in discord it's not something they were expecting to pursue.
At this point, I think the game is pretty much "Complete". They've already added more than their original vision (unlockable Sandbox mode, 2nd secret difficulty), and are shifting to another project.
As for your questions of size..... in Sandbox mode you can grow her much, much bigger..... check other forum posts here for notes on unlocking Sandbox and the secret difficulties.