I agree with you. The character had good potential in seasons 1 and 2. She was sort of the result of what I imagined would be Obi-Wan's wish for Anakin: 'Someday, young one, you will be given a Padawan exactly like yourself.' She could have been used to show another facet of Anakin's growth (or lack of growth if that's what the writers wanted) as a teacher, as well as giving him one more person, a little sister figure, to whom he became attached, and had to let go of. And given Yoda's speech in the movie, I assumed that's what was planned for her character. I wish the writers had continued down that route because it would have been awesome. As it was, by season 3, she was just in the way, a creation for Filoni to show off, and with no impact whatsoever on the larger story.