Trying to figure out if Leia should be a DP based on the attributes of a set is the wrong way to go, unless you know the one attribute that Official Disney uses. Here's how you can fall into the trap of figuring it out by looking at who's already an official DP...
Since the set is collectively called "Disney Princesses", one assumes that they must all be actual royalty. Or have been created by Disney. Or any female character in a Disney movie who is a princess. But then we realize those rules don't apply.
So, what the heck is the unifying trait which makes a Disney Princess a Disney Princess© ?
1. they fit "the princess mythology"
2. they can be -- and benefit from being -- marketed as part of the Disney Princess© brand.
And that's why they were created. The fuller story is on their Wiki page.
So, rather than have the princess character be marketed only in their own IP (e.g., Jasmine as part of the Aladdin franchise), she is also marketed as part of the Disney Princess© brand franchise for the synergy (gotta collect them all!) Minor princesses who don't bring value to the group or who won't get a big enough boost from the group get excluded (sorry Kida and Eilowyn). Other princesses who don't need the boost and are doing just fine on their own also stay out of the group (oh, hai, Anna & Elsa!).
So, that's their origin story and why there are so many exceptions to what would seem like expected and reasonable rules. In the end, they're a Disney Princess© because marketing says so.
Since the set is collectively called "Disney Princesses", one assumes that they must all be actual royalty. Or have been created by Disney. Or any female character in a Disney movie who is a princess. But then we realize those rules don't apply.
- Created by Disney: No. Most are folklore. Some by known authors such as Hans Christian Anderson for Ariel or Gabrielle-Suzanne Barbot de Villeneuve for Belle.
- Royalty: No. Some are married into royalty (Cinderella, Belle). And Mulan is neither royal nor marries into royalty. Mulan's presence pretty much means that just about any heroic female character can make it into the list of Disney Princesses.
- A product of Disney Animation: No. Merida is Pixar. And she's CGI, to boot. No classical hand-drawn Disney animation there. This opens the door for DPs to come from Marvel or LucasFilm or some other studio purchase in the future.
- The star of the movie: No. Jasmine is what we call a supporting actor in Aladdin which is about.... Aladdin.
- Human: No. This one comes up a lot when people wonder if any of the royal talking-animals will enter the group. And the reason this is no is because Ariel isn't human, she's only half human. Would this open the door for a future alien princess? A robotic sentient princess? Also, for a short time, Tinkerbell was indeed part of the lineup of Disney princesses, and she ain't human.
- Any animated princess: No. Princesses from Atlantis or the Black Cauldron don't make it. Elsa and Anna haven't made it.
So, what the heck is the unifying trait which makes a Disney Princess a Disney Princess© ?
1. they fit "the princess mythology"
2. they can be -- and benefit from being -- marketed as part of the Disney Princess© brand.
And that's why they were created. The fuller story is on their Wiki page.
So, rather than have the princess character be marketed only in their own IP (e.g., Jasmine as part of the Aladdin franchise), she is also marketed as part of the Disney Princess© brand franchise for the synergy (gotta collect them all!) Minor princesses who don't bring value to the group or who won't get a big enough boost from the group get excluded (sorry Kida and Eilowyn). Other princesses who don't need the boost and are doing just fine on their own also stay out of the group (oh, hai, Anna & Elsa!).
So, that's their origin story and why there are so many exceptions to what would seem like expected and reasonable rules. In the end, they're a Disney Princess© because marketing says so.