Maude Larrabee (Nella Walker)
Maude (David and Linus' mother) does the default cranky-old-lady thing and ineffectually disapproves of everything. It's a bit of a waste of the talents of Nella Walker, who had appeared in a whopping 117 films, starting in the silent era in 1929 and making a smooth transition to the talkies. Sabrina was her last movie appearance.
Oliver Larrabee (Walter Hampden)
Linus and David's father is a hidebound slave of classism; he's horrified that David wants to marry Sabrina (and later that Linus falls for her). Luckily, he's also largely incompetent ("You can't even get a little olive out of a jar!" as Linus says). If he were able to enforce his snobbery, he'd be a villain, but since he's a bumbler, he's just a comic bit part.
Miss McCardle (Ellen Corby)
She's Linus' long-suffering secretary. She doesn't do much except scurry around at his beck and call. She does get to look displeased about it though.
The servants on the Larrabee estate all cheer Sabrina on in her efforts to win David's affections. In part this seems to be because they all love her; she's grown up with them, and they want her to be happy. You also get the sense, though, that they're rooting for the team. If Sabrina can marry David, it means that those wealthy Larrabees aren't better than the servants, after all.
Baron St. Fontanel (Marcel Dalio)
Baron St. Fontanel is Sabrina's fairy godmother; he finds her in cooking class and points her in the direction of sophistication and a chic hairstyle.
It's sort of a shame that the Baron here couldn't be a Baroness. Sabrina is surrounded by men throughout the film—she shuttles from her dad to David to Linus. With her mom dead, she has no significant female friendships or relationships. The Baron (or Baroness) could have been an exception. But instead he's just another father figure mucking about in her life.
Elizabeth Tyson (Martha Hyer)
You have to feel bad for Elizabeth. She's incredibly wealthy. She's stunningly beautiful. And what does all that wealth and beauty get her? Nada.
She loves David, but he despises her. She wears a glamorous, low cut gown to the dance, showcasing her curves, and is effortlessly upstaged by Sabrina's boyish figure and elegant wardrobe. The film treats her with contempt, and at the end she's about to be married off to a man who can't stand her. If you're name isn't "Sabrina," Sabrina is a tough film to be a woman in.
Mr. Tyson (Francis X. Bushman)
You learn hardly anything about Mr. Tyson, the sugar cane magnate, except that he's willing to let Linus have control over their merged business in the name of his daughter's happiness. Magnate or chauffeur, the dads in Sabrina care about their kids.
Gretchen Van Horn (Joan Vohs)
Gretchen's the giggling, empty-headed socialite with whom David has an assignation on the tennis court, breaking poor Sabrina's heart. David probably has sex with her—and Sabrina knows he has sex with her, since Gretchen's mother has to go home without her.
When Sabrina agrees to meet David on the tennis court, then, she's probably hoping to, and/or expecting to have sex with him. Sabrina doesn't just want David; she wants to be Gretchen. (Luckily for the censors, Linus prevents such a scandalous state of affairs from sullying Hollywood's screens.)