Molting
Walburga didn't grow up at Grimmauld Place. She was born a Black, but so was her husband; Orion's grandfather, who was the elder sibling of Walburga's own grandfather, inherited the family home, in which Walburga didn't live until she married Orion. You'd never know this just from talking to her: the Black blood seems to run thicker in Walburga than it does in anyone else Druella has ever met.
Sometimes, Druella thinks that Walburga marrying a second cousin within her own family was inevitable, destined, fated. Walburga probably always liked being a Black too much to ever give up her name or her birthright.
And sometimes, Druella wishes it were as easy for her as it is for Walburga to be a Black—to put the family ahead of the people who are in the family. Everything would be so much clearer, cleaner, if Druella could have washed her hands of Andromeda the second she ran off with that Mudblood. But Druella can't draw lines like Walburga can.
Seeing Walburga tonight, you'd never know that she burned her son off the tapestry two weeks ago. She's in her element, eyes alight, dancing and gossiping and sparkling as if this were her wedding, not Bellatrix's, and her face only darkens when anybody in the room dares ask her about Sirius. "That blood traitor is no family of mine anymore," she barks every time, "and I'd appreciate if you didn't bring him up again." Then she closes her eyes as if to blink away the memory of him, and when she reopens them, the gleam of rage is gone, like it had never been present at all.
How many times did Druella write letters to Andromeda only to burn them without sending them? How many times did Walburga have to remind her that Andromeda wasn't a Black anymore? Druella doesn't know when she became this person who listens to her sister-in-law before her own daughter, but she's got two other daughters to worry about, hasn't she?—ones who followed the family example, who didn't walk away knowing full well what they were leaving behind.
Other times, she thinks Walburga's got it all wrong—that the people they burn away and leave behind should matter more than the family in whose name they do it. What's left of a family if you drain away all its members? Druella's already lost one child; she worries Narcissa will be the next to go, and all that will be left—
She never should have married Bellatrix off to the Lestrange boy. He ticks all the right boxes, but those boxes are hers and Walburga's—certainly not Bellatrix's. If any of her children was going to rebel, it should have been Bellatrix; Bellatrix was never meant to be the dutiful daughter; Druella never should have tried to mold her into such a—
All night long, after the ceremony was completed, Druella hasn't seen Bellatrix speak to her new husband. Not once.