Why is it called The Princess and the Frog if Tiana isn't really a princess?

Believe it or not, the title and story were inspired by a novel called "The Frog Princess," by E.D. Baker. In that story, Princess Emeralda kisses a frog claiming to be a prince, and accidentally becomes a frog herself, and they go on an adventure through the enchanted forest, trying to fix their predicament. They find out later that the frog was a genuine prince who was cursed by a swamp fairy as a baby, and the reason kissing Emeralda didn't work was because she was wearing a bracelet charm given to her by her fairy godmother that was supposed to protect her from curses, but it kinda...backfired. But they eventually fixed it. It was a cute story and far better than the crappy original fairy tale.

I remember how that one had a spoiled rotten blond princess who had accidentally dropped her golden ball into a well, and a frog claiming to be a cursed prince promised to get it out for her if she kissed him first. She tricks him into getting the ball out first and ran away, and the frog follows her around and gets her into all sorts of trouble before she finally eats some humble pie, learns not to be such a brat, kisses him, and they end up happily ever after.

The writers at Disney loved the E.D. Baker idea of the girl turning into a frog when trying to turn the prince back, so they took some ideas from E.D. Bakers' story, including part of the title. The thing was, though, (aside from copyright infringement) they didn't want audiences to think this was a story about an animal princess, so they had to change the title to "The Princess and the Frog" instead.