How in the world did I not know this?
According to MoviePilot.com, she was 14 at the time and played the part of the young Sarah Whittle. Sarah was the gal who was with Robin Williams' character when he disappeared into the game.
Now I'm going to have to go back and watch the movie again. Luckily it just happens to be on Netflix streaming right now.
UPDATE: Another reader pointed out that LBB was also on an episode of Home Improvement called "Mr. Wilson's Opus." She played Sharon, who was playing Juliet to Randy's Romeo.