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Toph's Vision
Here's how it would happen.
She would come home with Sokka (Katara and Aang would be out anywhere elsewhere, because it would conveniently just be the two of them). Her parents would go ballistic and point out everything that was wrong with Sokka, from his age to the teensy ponytail that graced the top of his head. Although it would be in character for him, Sokka wouldn't sheepishly tell her parents that he wasn't that bad because she had already warned and prepared him for this. Instead, she would smirk and tell her parents that she loved Sokka. He would nod vigorously in agreement because it would be mutual feelings by now—a part of their relationship that unfolded pretty quickly.
Her parents would approve, not only because they would suddenly and mysteriously realize that Sokka ruled, but that their daughter ruled most of all. So any dissent between her and her parents would cease to exist because the sheer awesomeness of two enamored and powerful people would over power them and their initial opinion.
Once they got married they would move into a fancy Earth Kingdom mansion (she was a Bei Fong, after all) because water never worked well with her. They would have two cynical, but intelligent children shortly after. Right after their predecessors, the children would become the greatest and most brilliant earth or water benders in the world whether they were disabled or not, and everyone would know it. All in all, they'd be one impressive family.
Now all she had to do was convince Sokka that she was a girl.