Women's Fiction is broader than pure romance. It can have a romantic element, but that is often not the primary focus. RWA defines women's fiction as, "a commercial novel about a woman on the brink of life change and personal growth. Her journey details emotional reflection and action that transforms her and her relationships with others, and includes a hopeful/upbeat ending with regard to her romantic relationship." 
The accepted definition of romance is developing relationship of two people [male/female or any of the BDSM combinations} which culminates with a happy (satisfying) ending. 
So while WF can have a romantic element, it's technically not pure romance...more mainstream targeting the female reader. Think Barbara Delinksky or Anne Rivers Siddons. They write women's fiction for the mainstream market, but are not considered romance writers. Women's Fiction writers who are RWA members write a male/female relationship into their stories.
With the advent of indie publishing so many of the pure guidelines have blurred. As I said, There are as many subgenres combinations as a writer can imagine and mash together.
Good question! Thanks for asking.