this Television Without Pity list) keep asserting that Ellie in Up is one of the most amazing characters ever. I remember when the movie came out, too, and everyone seized on this character as the great thing in the movie and how Pixar needs more female characters.
But my problem with calling Ellie a great character, much less a great heroine, is that she's not a character at all. She appears in the first 10 minutes of the film, has only a little dialogue, and then spends the rest of the film as the shadow of a memory. What are her main character traits? Well, she appears as an honorary boy for a few minutes, she loves Carl, she wants to go to Argentina and have adventures, and she never got to. She's what inspires the plot, but not as a person: as Carl's guilt-ridden memories. We never experience her outside of how Carl sees her, how Carl remembers her, what Carl says to her; we never see her except for how her life affects Carl's.
That's not a character. Certainly not a great heroine. More of a great emotional plot device.