Majestic, feeling particularly generous one day, says to her wicked cousin, Empress, "I promise to sell you my silver sparkle slippers for $350 unless I change my mind." The next day, Empress tells Majestic, "Here's the $350. I'll take those slippers now." Majestic says, "Forget it, you wicked thing. There's no way you're getting my slippers for any price."
Can Empress enforce Majestic's promise?