There can be crossover and women’s fiction can include a romantic element, however I don’t see romance as a sub-section of women’s fiction.
First women’s fiction is supposed to be written by women and plenty of romance are written by men. Also women’s fiction are about women’s experience but again plenty of romance nowadays are dual POV’s so as much about the man’s experience as the women. And there are also romance where both main protagonists are men so no women’s experience there.
I also think that lumping romance under women’s fiction runs the risk of reinforcing gender stereotypes that romance is for women and by default thriller and action are for men, which of course isn’t true.