I've noticed over the last few days that Helen is defaulting her pronouns to feminine. Even "daddy koala bear" is her/she.
I suspect the largest influence on this is direct conversation. I'm the person who talks to Helen most and (since she has I/me down fine now) I've long stopped talking about myself in the third person — and the person I talk about with her most is of course Camilla/mummy. Her playmates at nursery are fairly evenly mixed, but all her carers are women. And the majority of her playdates have been with mothers and daughters (Veronica/Rosie, Lucy/Rachel, Kat/Immi, Nadia/Frieda, Fiona/Leila) though she's now taken quite a shine to Parker and Dylan which may even things up a bit.
Like most English speakers, I have a strong tendency to default unmarked characters (human or animal) in books to "he". Similarly in pictures, people and animals are assumed to be male unless marked as female. I do my best to avoid this when talking to Helen, largely by defaulting unmarked characters/figures to female and by (when it's trivial) reversing gender-based role assumptions. So the bear in I Want My Hat Back is never referred to by pronoun and could be either male or female; I assume it's female and refer to it as "she". Helen's favourite zoo jigsaw puzzle depicts ten children, five of whom are marked as girls - by pigtails, a skirt, dresses, and a headband with a flower in it - while the other five are unmarked and presumably meant to be boys; when I talk about the puzzle with Helen, they are all girls. And (when I catch myself in time) I try to make any toy figures driving trucks or piloting planes women, while I default adult animals alongside babies to "daddy" unless that would be anatomically or ethologically impossible.
I'm not going so far as changing pronouns in stories (except in The Very Noisy Night, since Helen has a female "little mouse" toy), let alone inventing new ones or taking even more drastic measures, but I think Helen will get more than enough exposure to traditional assumptions about gender roles from the rest of the world that a little subversion can't hurt.