she hardly ever see the bright side of things. I mean she has one of the most comfortable, well provided life but she still whines about it.

I guess? She didn't seems to be strongly optimist or pessimist imo.

^

Definetely. She considers herself very unfortunate and complains a lot. She never tried to find something good about her suitors. Unfortunately, it's reletable. I am very pessimistic myself and complain a lot.

Heroines whom I consider optimists are Snow White, Rapunzel and Su from Mulan II. These three are very similar to each other. Snow White is separated from her beloved one and she manages to have enjoy herself. Rapunzel tried to find good about her life in the tower and found good about thugs. Su enjoyed Chinese landscapes and was excited by their beauty, despite being forced to the arranged marriage.

Niether? She seems more like a realist that just wants to get out of her situation, but her resolve is based in naiveté.

Whining about your life doesn't mean you're pessimistic, it just means you're ungrateful (which I really don't think Jasmine is, she just wanted something different), pessimism is more that you think you'll never have any hope, and Jasmine does think that one day she'll be happy with Ali or just being free. She's not optimistic either though, because it's not like she thinks everything will turn out great all the time.