Part of the reason Royal lost in 2007 was because of antagonism between various left wing groups. She may have made it to the run-off, but unless the Socialist Party has an open dialogue with the smaller left wing parties to secure their support, Mitterrand will remain the last left wing President of the country.
Left-wing division was really not an issue in 2007, quite exceptionally. Everybody in the left was in an "anybody but Sarkozy" mood, plus remembrances from 2002 were strong and the left feared to be ridiculed once again. Basically everyone except the few far-left loons endorsed Royal.
If divisions might have played some role, it's rather
inside the PS, since Royal managed to alienate almost everyone in the party with her "I'm not like them, I'm soo cool !" rhetoric. Yet, the major reason for the 2007 defeat was Royal's utter stupidity.