Yeah, Dona is kind of bitchy at first, but I get the feeling it comes from a place of insecurity and Yuna being an easy target. When Yuna stands up for herself, Dona starts to back off, and she becomes a good bit more civil. She still isn't the nicest woman in the world, but that's kind of just her personality.

If you think about it, Dona only has her lover. She's still trying to fight for Spira and sacrifice her life for others. Yuna is the well-known daughter of a High Summoner hero, she has Auron, her father's guardian, she has the worldwide support, she's like the "celebrity" summoner. I think Dona might be feeling overshadowed or inadequate when competing against someone who basically all of Spira is rooting for. And she also has a point, she makes it pretty far on her own with only one guardian and herself. That should be a testament to the fact that she obviously has some talent. She was probably just feeling like no one really gave a flying poop about her and the journey she was making and the hardships she was facing and the internal struggle of walking to your death. She still had to go through all of that, but with less overall support than anyone. That probably caused her to lash out at Yuna, which wasn't helped by Yuna's innocent, easy to pick on demeanor, but eventually she gains respect for Yuna and realizes she was being petty.

That Isaaru though