Okay, took me a bit to gather my everything, but here we go:
"You've always been naive"
For reasons that I think are sort obvious, also I fail to believe that naive is a word Clara would use to describe herself ever, not until Tommy brought it up at least.
“I don’t forgive him because of the memories, Lizzie,” Clara answered. “I forgive him because he’s nearly my father and because I know he cares for me as much as I care for him. Ruby and Charles know that. Jamie will, too.”
This one had reminded me of two things, so yeah.
“How about peace instead, Tommy?” she asked.
“Peace, eh? Ada told me you wanted peace, but that was nearly a week ago now,” Tommy said.
“Well, Ada should learn to keep her mouth shut,” Clara answered. “And I’m sick of fighting you.”
Tommy nodded. “You’re ready to a--”
“I’m not apologizing if that’s what you’re going to say.”
“Good,” he answered. Tommy wasn’t after an apology anyhow. “If you apo--”
“But I’ll consider a compromise,” Clara answered.
Tommy snorted. “And what compromise is that?”
“I’ll let you apologize to me... and I’ll admit you were right,” she said.
“Really?” Tommy asked. “You’ll let me apologize?”
Clara nodded. “And I won’t even tell anyone you did it.”
“But you can’t tell anyone I said you were right either,” Clara added.
“Would ruin your rebellious, independent sister facade, eh?”
“Yes, and if I talked, we’d ruin your cold, heartless, bad man facade.”
“Who says it’s a facade?”
"You can't be skipping meals, working all hours of the night—"
Clara raised an eyebrow. "You—"
"You're not me,” Tommy interrupted, fixing her with his steady gaze.
Clara scoffed, folding her arms over her chest and shifting her eyes beyond him to the fireplace. "I know.”
Clara was keenly aware of that fact, the fact that she wasn't her brother, wasn't nearly as clever or efficient or hardworking and she couldn't help but wonder why he was putting her through all the schooling when it should have been him.
Tommy and Clara have always had different ways of expressing their emotional extremes Tom's is loud and brash whereas Clara is very quiet and over-corrective The Small Acts is where I go when thinking about this but it also goes to the one chapter in the full Little Lady Blinders fic after Tommy tells her about Campbell's threat.