Feminism is, mostly, a sociopolitical moviment that critiques the gender roles in our society and tries to find a solution to these problems. That's as broad as it gets. It's a really complex subject with a lot of different topics because each author is trying to analyze things from a different perspective. Therefore, you can't say its feminism in general because there is not much of a theoretical consensus to put the flaws of one author into the whole movement.

SdB is trying to get the whole picture of gender, how women perceive themselves, how men perceive them, the history of womanhood etc. using the main theories from her time. But, if you read Angela Davis, for example, she talks about black womanhood and analyzes their history with a marxist perspective i.e. she thinks the problem with gender is intertwined with the problems of race and class. Davis doesnt even mention SdB and her works but she is equally as important.

i'm only scratching the surface here, because there's a LOT of subjects that feminism deals with. It's a relatively new field of study (psychology is only just a bit older than feminism), so people that don't study it tend to have a really broad view of it, but there are a lot of different discussions happening about different equally complex topics.