Take a close look at this button. It's very visually appealing to look at; the blue hues and circular shape combined with capital letters give off a calm yet formal vibe. More important than these graphic details, however, is Hillary's gender agenda. By using the word the 'her', Hillary draws attention away from herself. The voter is not with Hillary, not with the Clinton family, not the with former Secretary of State and 2008 Presidential Candidate. They are with her, the possibility of the first female president.
As Clinton is a Democratic candidate, the fact of the matter is that most of her voters do support gender equality, and most of them will deny a claim of sexism until their last breath. So what better way to get those voters on her side than to make not supporting her seem sexist. If you're not with her, then you're not with women in politics. You're not with job equality. You're not with supporting women. You're not with equal rights regardless of gender. At least, that's what this slogan is designed to make you think.
Another brilliant aspect of using the word "her" is that it creates a sense of unity among women. It's about seeing your own success and growth as a woman paralleled with hers. It's about getting someone that understands your struggles as a her into the White House. It's about all the little girls who will now have a role model, who can grow up to be just like her. It's about all the Republican women who might not be inclined to vote for a Democrat, but who are certainly inclined to get her voice heard. It's about the women who are willing to put aside their differences and come together to ensure that a him who hates hers doesn't get into office.
In using the word "her", rather than her own name, Hillary Clinton's slogan takes on a whole new meaning. It's a genius tactic to get all sorts of people on her side, by making the election a matter of gender and gender equality; rather than about whose policies are better than whose. It's about making the voter question their own morals - can they really call themselves a feminist, can they say they support women if they don't support her. Hopefully for Hillary, they can't.