NyQuil is a terrible thing, as I said. Never registered with me that it was the same actress. That shows her range, I'd say. She was typical of teen-comedy casting decisions, though, as she was a then-25-year-old playing a 15-year-old.
Loser, do rent the "MR" two-disc DVD set. If the musical numbers intrigue you, several of them can be seen on the second disc in continuous performance shots (and multiple camera angles), without the cut-aways needed to tell The Rest Of The Story.