Emotional abuse - an example from an Anne book

I recently listened to an audio version of Anne of the Island by Lucy Maud Montgomery. This is one of my favorite in the series. But amongst the camaraderie and cheer at Patty's Place and the happy ending for Gilbert and Anne, Montgomery gives a chilling example of emotional abuse. In this case, it is not between spouses but a mother and son. There are no blows or harsh words but manipulation, emotional blackmail, and the desire to control another human being in the name of "love." She writes a similar tale but between two sisters in Rainbow Valley, Chapter 31. In this case, it also involves a promise to never marry so the other party will never be alone.

This makes me wonder from what source did the author draw this storyline? Would this have been categorized as abuse in her day? I don't know, but Anne does call the antagonist "a cruel, relentless, deceitful old woman." I'm glad the plot ends well in both books, but in my opinion, the dynamic between the characters can't be categorized in any other way other than emotional abuse.

"Janet," he said, "will you marry me?"

The words burst out as if they had been wanting to be said for twenty years and MUST be uttered now, before anything else.

Janet's face was so red from crying that it couldn't turn any redder, so it turned a most unbecoming purple.

"Why didn't you ask me before?" she said slowly.

"I couldn't. She made me promise not to—mother made me promise not to. Nineteen years ago she took a terrible spell. We thought she couldn't live through it. She implored me to promise not to ask you to marry me while she was alive. I didn't want to promise such a thing, even though we all thought she couldn't live very long—the doctor only gave her six months. But she begged it on her knees, sick and suffering. I had to promise."

"What had your mother against me?" cried Janet.

"Nothing—nothing. She just didn't want another woman—ANY woman—there while she was living. She said if I didn't promise she'd die right there and I'd have killed her. So I promised. And she's held me to that promise ever since, though I've gone on my knees to her in my turn to beg her to let me off."

"Why didn't you tell me this?" asked Janet chokingly. "If I'd only KNOWN! Why didn't you just tell me?"

"She made me promise I wouldn't tell a soul," said John hoarsely. "She swore me to it on the Bible; Janet, I'd never have done it if I'd dreamed it was to be for so long. Janet, you'll never know what I've suffered these nineteen years. I know I've made you suffer, too, but you'll marry me for all, won't you, Janet? Oh, Janet, won't you? I've come as soon as I could to ask you."

At this moment the stupefied Anne came to her senses and realized that she had no business to be there. She slipped away and did not see Janet until the next morning, when the latter told her the rest of the story.

"That cruel, relentless, deceitful old woman!" cried Anne.

"Hush—she's dead," said Janet solemnly. "If she wasn't—but she IS. So we mustn't speak evil of her. But I'm happy at last, Anne. And I wouldn't have minded waiting so long a bit if I'd only known why."

From Anne of the Island, Chapter 34 - John Douglas Speaks at last.