There are nine playbooks in Death Comes To Wyverley. Not all of them need to be female, and a couple aren’t even human. However since Wyverley college is an all-female boarding school and many PCs will be students, the party is likely to be mostly young women.
More importantly the administration and teachers of Wyverley college are (almost) all female. Since we’re approximating Wyveryley College to the village in a “vanilla” Beyond the Wall game, Wyverley is a self-governing entity with its own hierarchy and responsibilities to students and staff. The position of governer lies with Mrs. Umbrade, the Headmistress. Two other teachers are mentioned — Miss Greenwood the Magistrix, and Miss Prionte, the Etiquette Instructor.
What about the world outside? At first glance gender roles Ancelstierre appear similar to early 20th century southern England, given the segregation of boys and girls in schools (note that Prince Sameth attended Somersby, which isn’t on Mogget’s map). We don’t see a lot of the country south of the Wall; it does seem that the soldiers guarding the Perimeter are predominantly male, but we don’t get long enough with them to properly tell. Certainly we can argue that Ancelstierre’s implied early 20th century mores are there (as a literary device) to provide contrast to the Old Kingdom’s more egalitarian attitudes to gender roles, e.g. Clariel and her mother Jaciel.
The women of Wyverley do receive a rounded education not only in Literature and Etiquette but also Magic, Science and Fighting Arts. This is partly because some of the young women will be daughters of Old Kingdom families where magic is actually relevant and useful. At the same time daughters of Ancelstierre must be attending the college, and Wyverley is an opportunity to subvert these gender roles in an alternate 20th century setting. We should note however that the women of Wyverley, as well as many of Garth Nix’ principle characters are all in priviledged positions; even if the rich families of Ancelstierre and the Old Kingdom do intend their daughters to be educated in this manner and take up important positions later in life, it says nothing for the gender division for the rest of society on either side of the Wall.
A final remark about gender portrayal in this series: note that Sendings and Free Magic creatures are essentially without gender, but they do identify as male or female — the Disreputable Dog and Az are both “female” magical creatures, for example. This should be a consideration for a GM building adventures.
Like any Beyond the Wall game, the Village is defined and the Outside is there to be explored. Therefore the only certain point to make here is that Wyverley College is a matriarchy, and the various relationships arising from the Playbooks will reflect this. Beyond the Walls of Wyverley College the world should be a mystery.