She had posters hung up at all her stops with that slogan, sold t-shirts on her website and at her rallies with that slogan, hell they even were peddling caps and keychains with that slogan. I don't think at that point it really matters who thought it up, she adopted it as her own and just showed how fucking arrogant she was when she started hawking it instead of condemning it.
And now thanks to Wikileaks and an unnamed DNC staffer we know WHY she was so fucking arrogant, it was because she knew she was gonna win the primary before the first vote was ever cast. After all with the DNC handing her the debate questions, the press running major stories by her, and several of the largest media outlets running interference for her how could she not? But in the end it just showed the hubris of HRC and the DNC and how out of touch with anything not in NYC or CA they were because all one had to do was look at her approval ratings to know she didn't have a chance in hell, NOBODY has EVER won the POTUS with approval ratings even half that low. Mitt Romney didn't even score THAT low after his "48%" comment, she was so hated that she scored worse than Mittens at his lowest before she even opened her mouth and said a single word!