That is a very interesting character and is the one I chose for my first Deadfire pt.
She is a human that escaped the Deadfire Archipelago after her (royal) family was murdered (let's assume there is at least one human kingdom there, but not in the area we see in the sequel, since it doesn't exist in the game). Think of her as Arya Stark, from Game of Thrones, but from a royal family that was completely murdered.
After that she went to the Dyrwood and became a priestess of Skaen because she thought her family was oppressed (that is how she sees it! ). She was cruel only with criminals and people who caused her trouble and although I avoided the benevolent disposition as much as possible, she was actually a very good person.
As the game progressed she got disappointed with Skaen and abandoned her class (in Deadfire she is an assassin). Being an aristocrat, she had an interesting conversation with Skaen just before the game ends. He didn't acknowledged her as a one of his priests and said that if was not for Woedica he would make her suffer for oppressing others.
Skaen willingly submits to Woedica, so he has no right to talk about oppression and that was the last straw in my character losing her faith.
(Besides, the Scale Breaker Talent is multiply useful, and I think you get one more Adra Dragon Scale from killing the beast as opposed to cooperating.)
That is a good reason to fight the dragon.