^ Well, Brenda was staring at the screen but at the same time, she was turning and looking at Jim and Cindy who was so happy for Brandon. So, why didn't Jim and Cindy see Kelly? Maybe they were concentrating on Brandon. Oh, the possibilities.
It's weird; it is to believe that Dylan didn't see her at first. He told Nat that he has to go to the bank. Right when he got up, they showed Kelly in the audience. In fact, when Steve saw her, he said "Hey, I could just sworn I just saw Kelly Taylor," Dylan turned and looked around thinking she was at the Peach Pit.
But when Steve told Dylan that he was in the stands, they showed Kelly again on TV (or least part of her because someone sitting in front was blocking half of her). I guess Dylan didn't believe that was her.