Disclaimer: I don't own Sofia the First or any character from the series. I don't own any other Disney characters either.
The Stepmother Gathering
Queen Miranda of Enchancia was having a good night of sleep when she suddenly found herself inside a mysterious room she'd never seen before. "We've been waiting for you, Queen Miranda." She heard a mysterious voice say. Looking around, she saw two figures: one was a regal-looking woman wearing a red dress and the other looked like a beautiful Queen but Queen Miranda didn't recognize her from anywhere, assuming the other Queen was from a Kingdom too far away from Enchancia. "Excuse me but, who are you?" Queen Miranda asked.
"Allow me to introduce myself, Your Ma…" The lady in red started introducing herself until she was interrupted. "Let the royals speak first, you low-class noble. Greetings, Queen Miranda. I am Queen Grimhilde."
"Snow White's stepmother?" Queen Miranda asked in surprise.
"The very same, Queen Miranda." Grimhilde explained. "And this one with me is Lady Tremaine."
"Cinderella's stepmother?" Queen Miranda was even more surprised.
"Exactly, Your Majesty." Lady Tremaine replied.
"Does either of you know what I'm doing here?" Queen Miranda asked in hopes of obtaining answers.
"We're here to teach you how to be a perfect stepmother." Queen Grimhilde explained. "With our help, you can get rid of your stepbrats so your own daughter will become Queen of Enchancia."
"Why would I care about which one of my children becomes Enchancia's next ruler?" Queen Miranda asked with a frown. She didn't like the idea of becoming a wicked stepmother.
"Don't you favor Sofia over the children from your husband's previous marriage?" Lady Tremaine asked with a malicious smile.
"I don't play favorites among my children." Queen Miranda gently argued. "I gave my word and I don't care about whatever loopholes you exploited while making promises to Cinderella's father."
"Queen Miranda, if you'd rather have your daughter marry into another Kingdom and become Queen there, I can give hints on how to make sure your stepdaughter won't get in the way." Lady Tremaine suggested.
"Don't mind her, Miranda." Queen Grimhilde intervened. "She can't even keep the meddling stepdaughter locked away during the crucial moment. I can teach you how to make poisoned apples."
"What for?" Lady Tremaine arrogantly asked. "Princess Amber knows several Princes at Royal Prep. Certainly one of them would kiss her."
"This dream is going too far!" Miranda frowned. "I'm waking up." She then pinched herself and woke up. 'What a weird dream.' She thought once she found herself at her bedroom with her husband. 'At least Rollie didn't wake up.' She then resumed sleeping. Meanwhile, at another dimension, Grimhilde and Tremaine were upset they failed to convert another stepmother into wickedness. "We should have given up when the woman with the green-haired stepson declared she'd no longer read fairy tales before sleeping." Lady Tremaine commented.
I had this brainstorming me for a while.