I kind of ran out of drama there towards the end. The story centers around character: Claire the perfect ice queen. She’s not really an ice queen: she’s very superficially warm and friendly, which is what makes her a great posh waitress. But nobody ever gets very far with her. She has moved to Atlanta and made a lovely, classy life for herself; so when Donna, who’s trashy and a liar, makes her way into Claire’s life, Claire is at first torn, between a human connection and the potential threat to her classiness Donna represents, then angry because Donna turns out to be a grifter/blackmailer.
There’s another reason, down deep: Claire is jealous of Donna for being pregnant. Maybe Claire can’t get pregnant, or maybe she did and gave a child up for adoption long ago. So when Claire finds out that Donna’s not pregnant, and is faking it because it’s making rich Bruce want to marry her and take care of her… no, it’s just not a strong enough motivation for murder. It’s motivation in that Claire figures out that if Donna is going to fake being pregnant, she’s going to mess up Claire’s life, too. But why is Donna faking the pregnancy, if once she meets Alex she decides she wants to trade up? It’s just too complicated, so that detail needs to come out. Or maybe it’s Elle who lies, and who tells Alex that Donna’s not pregnant because she figures it will make Alex think twice about taking up with her. This adds additional pathos to the story because Claire (offscreen) can confront Donna: “y0u’re a big old liar and you’re going to mess with MY life, too,” and then Donna hotly denies it, and a fight starts and Claire takes her down more or less by accident.
Or a still better angle: Claire, when she came to the city lo these many years ago. left behind a husband and a kid in the rural hellhole. She just walked out one day. The kid, or the husband, is ugly or disabled or somehow problematic. Claire is still technically married: she can’t ask for a divorce because she doesn’t want her old life to track her down. Claire’s not her real name, either. So it makes more sense to have Donna show up at the restaurant without having got back in touch with Claire beforehand. Claire is confronted with decompartmentalization at work, which is what makes her so upset.
Now the conflict makes more sense: Donna has money, in the form of Bruce–and more, if she can trade up to Alex. And that’s what Donna wants, is entry into Claire’s classy world, in order to find a better-looking, wealthier sugar daddy. Claire a) knows Donna can’t pull it off, b) doesn’t want her classy friends finding out just what trash she used to be, and c) doesn’t want the husband tracking her down, for a host of reasons: she owes him child support, he’s just an embarrassing redneck, whatever. So Claire is mad because Donna busted into her life, she’s worried because she doesn’t want her old life catching up with her, and then when she hears (from Alex) Elle’s lie that Donna isn’t really pregnant, she realizes that with Donna around, she’s always going to be under a threat.
So what tips D/M off is the neatness of the crime. Someone calls Donna: this turns out to have been from someone who is a regular patron of the restaurant. Two hours later, Donna is dead in some very neat way: no blood. But Donna’s a slob. D/M keep confronting Claire with evidence about her past, but she won’t budge; until she finds out that Donna really wasn’t not pregnant. Then her nostrils flare again.