Once the truth comes out about how hillary has savaged women all over the world,here by helping Bill savage the women he raped here in the US and worldwide by not helping women who are savaged by the threat of islam and how it treats women. Once enough women discover just how much disdain or outright hate hillary has for other women they will run away from her in droves.
I'd guess that is 15-20%, at least. You will never go wrong by underestimating the intelligence of the public.
IMO race and ethnicity have more to do with the women's vote than gender. When you take a look at the 2012 exit polls, Romney won the white woman's vote 56% to 42%. They comprised 38% of the electorate.
Romney lost the black women's vote 96% to 3%. They comprised 8% of the total vote. Romney lost the Latina vote 76% to 23% and they comprised 6% of the total vote. Other women and men combined (Asian, and mixed race) voted against Romney 66% to 31% and they comprised 5% of the total vote.
When you see that Romney lost 19% of the electorate by such wide margins, it skews the women's vote, which Obama won 55% to 44%. What the Reps are facing is the loss of minority women's vote, not women in general. If Trump were able to win a greater percentage of the white woman's vote, he would more than negate Hillary's advantage.