Oh Sadie; don't you know we love you?
Let us list the ways. Sadie has the quiet strength of her father and the adventurous streak of her mother. She's the peanut butter to Bessie's jelly, the Keenan to her Kel, the Superman to her Batman. And that's not even mentioning her own prodigious accomplishments in the professional world. All in all, we'd say that Sadie has this whole life thing on lock.
Like her father, Bessie believes in speaking so softly that no one realizes you don't have a big stick. In their eyes, the "way to succeed was [...] to be better at what you did than any of your white competition" (5.18.2). If that doesn't work, then it's time to "sweet-talk the world" and "play dumb," beating blatant discrimination by defying it in the most pleasant way possible (1.2.2). That's vintage Henry Delany.
This pleasant yet passive demeanor becomes an important part of her relationship (more like partnership) with Bessie—Sadie is the brains behind the operation and Bessie is the muscle. That's easily apparent in their family dynamic: when the kids need to make a decision, "Sadie had the last word, but Bessie kept everybody in line" (5.15.15). Remember the time that Sadie and Henry get into a passive-aggressive duel over who should kick Frank out of the house? That kind of thing would happen a lot more if Sadie and Bessie were both as sweet as molasses.
Sadie's a lot like her mom too, but you might not realize it at first. Like her mother, Sadie ventured away from a stable family life for even greener pastures. For her mother it was St. Aug's in Raleigh; for Sadie it was New York City, where the "bridges and buildings were on a massive scale" "beyond [her] imagination" (5.15.3). Sure, Sadie had the benefit of Bessie (and her other siblings) sharing her journey, but Sadie's status as the oldest girl makes her the de facto head of this satellite family.
But it's not until Nanny moves to New York that we fully understand their similarities. While Bessie the Grouch stays at home doing lord knows what, Nanny and Sadie go on crazy adventure after crazy adventure. They travel to Atlantic City, L.A., England, Russia, and Hyrule—okay, that last one might not be true, but you get the point. To be honest, we never see Nanny happier than when she's riding in a biplane over Niagara Falls "having the time of her life" (5.24.18).
Nanny's death is tragic—and Sadie is devastated by it—but the one silver lining is that it forces her to become herself. Maybe it's that Sadie finally realizes that she and Bessie are on their own. Maybe it's that her strict upbringing created an early innocence that never fully faded away. Or maybe the death of her mother simply reminds her that her own time is limited.
Regardless, this late-life bloom has a profound impact on Sadie. She stands up to a gang of unruly kids, which would have never happened before. Sadie was never quite a push-over, but she certainly wasn't one to call out a bunch of kids for loitering. Bessie would've; Nanny definitely would've. Maybe Sadie has more of that fiery Logan blood in her than we thought.