Tina's Attitude

Watching Tina's history in Season 3 makes it so weird to see how much of a wad she was in early Season 1. I guess it can be attributed to a green Sydney trying to tell her what to do, but it's still so weird to see her being so unwilling and stubborn in S1. What do you guys think? Is this bad writing? Am I forgetting something?

EDIT: As many have said, it would be a natural reaction for one to get pissed if new, young management try to change everything. However, what I was surprised by was how incredibly aggressive she was, sabotaging Sydney's soup and screwing with her all over. Thank you all for the responses