At least she watched the debate. Not like those people who were interviewed on the street before Debate 2 and claimed they already had watched it.
Without further info, I rather doubt this. Probably watched something like Comedy Central and assumed VP Biden was the Republican based upon PREjudice (def: opinion formed beforehand: a preformed opinion, usually an unfavorable one, based on insufficient knowledge, irrational feelings, or inaccurate stereotypes). We tend to forget how our youth today are swimming in a liberal progressive ocean. Education, media, entertainment all incline them to the left.
A real world example of how this concept can be carried further into politics and elections is the Argentina Government's decision to lower the voting age to 16. Here in the US, there is an activist movement called National Youth Rights Association that calls for similar moves here. I have no doubt as to their political inclinations and funding. FYI they also advocate for lower drinking and curfews.