That looks really interesting, thanks for the link.
DD - also 9 - educated herself about feminism thanks to the Jacqueline Wilson book Opal Plumstead which is about a girl who becomes a suffragette. She really likes the Girls are Best book by Sandi Toksvig which is linked to on the Amazon page.
There are two other good fiction books as well. One is called Polly's March by Linda Newberry and the other is My Story: Suffragette by Carol Drinkwater.
But there aren't enough books, at least as far as DD is concerned, so would love any more suggestions too!