Well, it could technically be the plural 2nd person, but it would make less sense than the "vos", which is perfectly accurate as far as I know (I'm no philologist, though). There is one occurrence of the "usted" (which wasn't used then) that has slipped: "espero que este trato reciba su bendición" (the equivalent of "would you be interested in a trade agreement with England" for Spanish, only with a mistake; I don't mind it because "usted" sounds already formal enough to me).
As of now, what she says would only have sense if she was speaking to a group of people (or as a parody of the speech of that era); I think the same applies in English, it's called the majestic plural.
If anything, they've made a mistake for her presentation: she calls herself "Isabel de España", while she should say "Isabel de Castilla"; only her grandson "Carlos I de España" (as he was called in our country) started using the term officially for the crowns of Castilla, Aragón and Navarra.