The Lady Arwen Undómiel, Yeah, that was weird. The whole swords-turning-blue thing was weird. The whole green mist thing was weird, for that matter!!
wizardjna, You are correct, Jill is not mentioned until The Silver Chair. Eustace and Jill don't meet in Narnia, though, they meet at Experiment House, the school they both go to. It is obvious from the first chapter that the two already know each other, although they have not communicated much (Eustace talks to Jill about the change he underwent that summer, comparing his behavior now to the kind he had last year in school, and Jill agrees that he was a brat before.) Having that knowledge, the director, I suppose, decided to add that little line in preparation for the upcoming Silver Chair, so that people would kind of recognize who Jill was. (if it were coming up) VDT's poor box office performance in comparison to its predecessors LWW and even PC, and also the complication with the rights issues (see the Narniaweb news page) have led to the situation we are in now, where we are not sure if Silver Chair of Magician's Nephew will be next, or if any movie will be made, so that line may prove unnecessary with time.
Personally I think that line was extra, but it's there, so nothing can be done about it.