Are you a personal victim of hers.... Duchess? 
My skirt is still where it should be, thankfully. 
I can get behind the childish pranks and sabotage being a form of defiance and her way of screwing with the rich people. I don't really consider that fighting back though, and definitely not for the benefit of all the poor, little people. Killing ******* employers is a questionable way of helping as well. Sure, the jerk is now dead, but so is the little person's source of income. And your boss doesn't have to die for you to be able to switch jobs. Unless the hope is that the mean rich person gets replaced by a nicer one, nothing is gained.
Nothing Sera does or says showed her as the defender of the common people she is claimed to be. She actually disapproves of what I can recall as the one big choice that potentially has a big impact on city elves: helping Briala to get in power. Sera's reason for disapproving is skepticism about Briala sticking to her promises and intentions once she is one of the big shots. And sure, power corrupts. It remains to be seen how much Briala can and will do to improve the lives of the elves in Orlais. But out of the three available candidates? Celene has already ordered an Alienage purge before or something along those lines. Gascard just wants to go to war with Ferelden again and is unlikely to have the elves high up in his agenda, if anywhere at all. Briala at least seems to care and willing to try something. But Sera never even uttered a word about those poor little people and what the ruler of Orlais could do for them. Maybe those elves are too little for her? Because they have a vhenadahl tree and try to uphold a tiny bit of their elfiness?
Ultimately she's a very random character. Too random to seem believable to me. A character can be immature, rude, intolerant, a hypocrite and much more and that's fine. It won't make me like the character but it doesn't mean they're bad. But Sera is a lot of those bad traits mashed together, the mention of some more positive traits she then doesn't live up to or act on, and made whole with an incoherent speech pattern. Not a very likable character and, worse, not a very good one either, as far as I'm concerned.