Here's something you might not know about Disney movies. They all pretty much have one, two, or maybe even four sequels. A lot of those sequels were made in the time of "straight to VHS" or "straight to DVD" movies. The thing is that they were animated just as well as the main movies, but I'm guessing Disney didn't want to ruin their brand by bringing them to the theaters, yet they still wanted to make easy money. 'Mulan' fell victim to that process, which is why 'Mulan II' exists.
The first 'Mulan' movie came out in 1998, while the sequel came five years later. Given the story of the first movie, I don't see a sequel being very impactful. In the first one she pretends to be a man to join the army. What's she going to do in the sequel, get gender reassignment surgery?