He'll probably do that for all the girls he's wronged. Song gets two ostrich-horses, a sack of gold, and a note of thanks for 'donating' her ostrich-horse to the cause. It'd be an outright apology, but Zuko needs to keep some face with the troops. Mai gets a cushy job that suits her well and lets her order around soldiers, because regardless of everything else, he did use her. Jin gets her own tea shop in Ba Sing Se.