Begum Arshi can be called a feminist because of the way she conducts herself.
In our society, women are not supposed to talk about sex. They are not allowed to be open about their sexual desires. They are not supposed to make sexual advances or be flirtatious with men.
Men are supposed to make the first move and women are expected to not accept that move easily. Otherwise they are considered characterless.
Begum breaks all these stereotypes and gender norms, by showing that it's okay for women to express their sexual desires, be flirtatious and to make the first move instead of waiting for men to do that.
Begum's this mentality is not liked by people both inside and outside the house, and because of this she's considered loose and immoral?