This is just a guess, but the capital letters would seem to be for exaggerated emphasis of what she's being reprimanded for.
I'm thinking “leverbe” is probably a typo for “le verbe” in either variant of sense A. 3. (both used in the singular) listed over at the
CNRTL's Lexicographie: an expression of thought, or a callback to the manner in which Elisabeth expressed herself (with the implication that she should improve her attitude by expressing humbler sentiments).
If that's the case, then the sentence would be roughly: “Elisabeth, as soon as we get back, you'll write the expression Pray the good Lord to Help me no longer Be so Impertinent.”