rub it in

最初はアンを引き取る事を渋っていたMarillaは気持ちに変化があったことをMatthewに告白(own up)しました
"...I can't imagine the place without her. Now, don't be looking I-told-you-so, Mattew. That's bad enough in a woman, but it isn't to be edured in a man. I'm perfectly willing to own up that I'm glad I consented to keep the child and that I'm getting fond of her, but don't you rub it in, Matthew Cuthbert."
"I-told-you-so" と言う表現は面白いですね。　"rub it in" はこの "I-told-you-so" の態度の事を示している様ですがどうでしょう。　連語や慣用句を辞書で調べるのは厄介な場合が多いのですが、"rub it in" は慣用句として次ぎの説明がありました。
・Dictionary.com: Informal. to emphasize or reiterate something unpleasant in order to tease or annoy: The situation was embarrassing enough without having you rub it in.
・Wiktionary: To add insult to injury; to emphasize one's strengths or another's weaknesses in a manner that degrades another.; I know you're a better painter than I am, but you don't have to rub it in.
・Cambridge Idioms Dictionary: if someone rubs it in, they keep talking about something that makes you feel embarrassed or upset I know I made a mistake, but you don't have to rub it in.
塩を傷口にすり込むことを想像すればこの慣用句 "rub it in" は覚えられそうです。