Perhaps she is curious. Perhaps she has some masochistic feelings that are vented through the fantasy. Pornography breaks cultural and political stereotypes, so that each woman can interpret sex for herself. Anti-feminists tell women to be ashamed of their appetites and urges. Pornography tells them to accept and enjoy them.
Pornography provides reassurance and eliminates shame.
It says to women 'you are not alone in your fantasies and deepest darkest desires. Right there, on the screen are others who feel the same urges and are so confident that they flaunt them. Pornography can be good therapy. Perhaps they are away from home, recently widowed, isolated because of infirmity. Perhaps they simply choose to be alone.