The anwer to this mystery is that Garry and Mr. Jason are innocent and Susan is guilty of the crime.
Garry is innocent because he is a fireman, and he would not set a fire in the restaurant just so he could put it out. And he would not set it because he might hurt Susan. He was trained to respect others.
Mr. Jason is also innocent because he would not want to set a fire in his own restaurant and have to pay for all the damage. He had no insurance. He cannot fire Susan, and she is making things difficult for him, but that does not give him a good motive for the fire.
Susan is guilty of this crime. She wanted to destroy the restaurant because Mr. Jason was mean to her. She loves calendars, and she was the one who put the calendar papers on the kitchen floor. She was missing the calendar papers that were found. The bubble bath soap bottle was full, so she lied about how she loved bubble baths. She hates the rain and being wet. She was really a gymnast, and she lied about being hurt when she tripped over the chair.