She freed the slaves in Mereen, she took revenge after they crucified slaves, can't remember were they kids?,. Afterwards under pressure she opened the fighting pits and was even going to marry one of the fucking nobles until the harpy's intervened.
Her actions in kings landing cannot be justified, but thats not the point, it's the lack of story for her downward spiral into madness thats annoying. Lazy, rushed writing has given an unsatisfactory end not just to Dany's character but also virtually every major character left standing.
See the Kit Harrington interview? Sum up the ending of game of thrones in one word Kit? He answered disappointing, I feel the same way.