Seth Rudetsky's Head Vs. Chest 101...

I'm not entirely sure I agree with his assessment here, because though Andrea McArdle is using her chest voice, she does mix some head voice in on the higher register. If she didn't it would come out really thick and forced as when you TRULY use your chest voice your vocal chords stay thickened and closer together. Pure head tone the cricothyroid muscle comes in to play, stretching the vocal chords, thinning them and separating them. That is how she gets that resonate tone at the top of the song! Either way, it gets the idea across.