Before becoming Hitchcock's secretary, she used to go to a school in Rocky Beach. She was a number of grades ahead of The Three Investigators. According to Bob, she used to help the teachers and "boss all the little kids around".
When the Jupiter Jones was, somehow, able to convince the guard of the World Studios that he was Alfred Hitchcock's nephew, Larson came to know about it. Larson didn't allow Jupiter and Pete to meet Hitchcock at first. Jupiter, however, used his impersonations to convince Larson that Hitchcock would definitely be pleased and "would be interested in seeing the display of his acting talents", and was able to meet Hitchcock.
She was described to be very bossy by Pete. Bob also remarked that if Larson was Hitchcock's secretary, they should "better forget meeting Hitchcock", and that "three armored tanks couldn't get past her".