V3 P4, 12%
"Hein, I intend to ask His Majesty..."
I assume Hein is a nickname, but including it here just in case it should instead be Heinz
23%
Come to think of it, there was Priest Nax, Prince Robur, and a boy who was the lady's classmate there with her"
Should that be Prince Regulus? (Or if instead her brother turned up, Lord (/Marquess, or other subsidiary title) Robur?)
"Since I made a donation... you ought to provide commensurate assistant"
Assistant -> assistance
"What?! Duchess Rober?!"
Rober -> Robur
35%
"Ever the high priest. No sooner had she spoken than he deployed a barrier spell around herself"
She -> he, herself -> himself
55%
"That day, when that good-for-nothing Second Prince got a wonderful fiancee far beyond his station but couldn’t even manage the simple task of meeting her face-to-face for the first time, it confirmed once more what a failure he was."
I don't think this sentence quite makes sense as is, unless Duchess Robur thinks that the Second Prince is also a good for nothing, and that Lavi is a wonderful fiancee. Instead, perhaps:
"That day, when that good-for-nothing got a wonderful fiancee of the Second Prince, far beyond her station, but couldn’t even manage the simple task of meeting him face-to-face for the first time, it confirmed once more what a failure she was."
"I’d ripped open that failure’s belly with my signature magic. But I didn’t kill him. I left my son, who was learning healing magic, by that failure’s side."
Him -> her
65%
"She does meet with the former prince outside sometimes, doesn’t she?”
I think this is referring to Heinz (since Prince Regulus is neither former or, I gather, hasn't visited the nearby atelier). I'm not fully on top of terms for nobility, but prince should only fit if the son of a Royal Duke (which I can't recall if this is the case here or not). If not, perhaps Lord (or even a subsidiary title like Marquess) might fit better.