Will this strategy work? I think Royal's main strength at this point is her celebrity. It is also her main weakness, since every gaffe she makes, such as the PNUD flap, is immediately magnified by the press coverage that automatically attaches to her every move. She needs to keep herself in the public eye constantly yet ensure that the coverage actually amplifies rather than diminishes her image. It's a tricky business, and she hasn't been particularly adroit at it in the past, in part because her positions on key issues seem, bluntly speaking, to vacillate. Sarkozy also exploited the media, but he cultivated great message discipline and hit upon a few simple themes to encapsulate what he was about. Royal hasn't yet managed to identify the issues that are to define her candidacy.
On the failure of Désirs d'avenir to extend its reach beyond the PS, see this on the departure of its former head, Jean-Pierre Mignard.
ADDENDUM: Royal captures my thought in her own words:
« Ce n'est pas mon problème, je n'interfère plus dans les sujets internes au Parti socialiste. Moi, je m'occupe de ma région et de travailler dans le cadre de Désirs d'avenir. Je ne m'exprime pas ni au nom du PS ni pour protéger le PS. »