"he doesn't want to piss her off any further" In my opinion, you've nailed it exactly.
"wouldn't she have been distraught when she talked to her mother on the 24th?" Very good question. I never heard of her mother saying she sounded distraught, but I DO remember that sometime her sister Amy (the hairdresser) said that when Scott and Laci stopped by her salon on the evening of the 23rd, there was some tension in the air, and Laci shot out the door without waiting for Scott, or something like that.