When the protagonist, Thorby Baslim/Thor Rudbek, gets back to Earth after a really complicated life elsewhere in space, one of the people who greets him is his first cousin once removed, Leda Rudbek. (I'm not quite sure how she came by the Rudbek name, as her mother was the younger sister of Thorby's mother's mother, but she's Thorby's mother's first cousin.) Heinlein is condescending toward her—he points out that she can do arithmetic "slowly," and not being able to do mathematics counts as not being fully human in Heinlein's novels—but in fact she plays quite a striking role in the events that follow.
Thorby finds himself being encouraged to behave as an idle rich boy, and kept carefully isolated from the actual doings of the Rudbek corporate empire. It's Leda who explains to him that he's the heir; and later she tells him about problems in the corporate management—problems for which her stepfather, John Weemsby, who has been acting as general manager since Thorby's parents disappeared, is responsible. She advises Thorby to hire a specific lawyer, and helps him arrange to do so secretly. He thanks her, and she answers,
"'Thanks' he says! Thor, this is for Rudbek."
She explains that she's a Rudbek (she has shares of stock that her uncle gave her when she was born) and her father isn't. And later, in the climactic scene, a shareholders' vote to decide whether to put Thorby in charge, she shows up at the meeting, having cancelled the proxies held by her stepfather, and casts the deciding votes for Thorby. Weemsby rebukes her, calling her "Leda Weemsby," and she answers "My legal name is Leda Rudbek." And that costs Weemsby the job he's held for a decade or two, and presumably breaks all ties between them.
So what Heinlein shows us is that Leda is the actual agent of Thor's coming into his inheritance; that she's actively opposing the man who raised her; that what drives her to do so is pride in her family. And when she sets things up for him to talk with the lawyer, she tells him, "I've had a sleepless night and I'm convinced they mean business. So I had to make up my mind." There's a story there, and a dramatic one, that Heinlein is telling the readers mostly by implication. Perhaps he thought it wouldn't be very interesting to the teenage boys he was writing for, but when I read Citizen of the Galaxy now Leda is interesting to me.