After catching Jess coming out of Rory’s bedroom, and Rory’s bracelet coincidentally turning up under her bed when she’d already looked there numerous times, Lorelai puts one and one together and draws the obvious conclusion that Jess had Rory’s bracelet and had secretly returned it.
She immediately accuses Jess of stealing Rory’s bracelet and keeping it out of jealousy towards Dean, not caring that he was upsetting Rory in the process. Lorelai doesn’t bother trying to get all the facts, because Jess didn’t deliberately steal Rory’s bracelet, but held onto it after she lost it. He didn’t know it was from Dean, and was not trying to cause trouble between Rory and her boyfriend by keeping the bracelet.
She makes the mistake of attacking Jess as if she is a teenager herself, calling him a “little jerk”, rather than behaving like a concerned parent. This mother-daughter relationship where Lorelai tries to be both a mom and a best friend often goes wrong when she tries to be a friend when she should be a mother, and vice versa.
Lorelai has a temper and tends to go off halfcocked, especially when it comes to safeguarding Rory. Jess has no hesitation in talking back to her, and this episode will leave Lorelai with deep distrust and a simmering resentment against Jess which will explode later in the season.