A lot of the modern novels have opted for the conflicted relationships hiding feelings. For instance, in the Pendragon series, Loor originally believes Bobby is weak and incompetant, but after a while and they get to know each other better, they end up falling love. Harry Potter is a much more well known example, as Ron and Hermione bickered and put each other down a lot, but were actually hiding their feeling for each other.

Aang is also the first friend Toph's ever really had, and is the first person really able to draw her out of her "shell". She obviouly has a soft spot for Aang.

Toph is slowly trying to assimilate herself into Aang's lifestyle. She's gone from despising Appa to trying to understand him, and she was crushed at being unable to save him.

She's also a good person to get Aang to be more assertive. As the Avatar, he needs to take part in issues instead of watching from the sideline, and Toph's a good person to teach him that.

We haven't seen a "Storm" like episode really for Toph (But we have for Zuko and Katara), and it could very well be similar to Storm and CoTL with them getting trapped and are forced to simply talk and understand each other more (For Taang and Zutara), similar to "The Storm", except they don't really like each other all that much at first