Just try to make sure that she doesn't see you lose your patience. Obviously I don't know your specific situation. But I used to be a 15 yr old with a somewhat shitty attitude due to my own situation and every time that my stepmom lost her patience or acted like she was fed up with me, it only made things worse.
Although, she is a pretty horrible person (still) and would say really horrible things to me (only when my dad wasn't home to hear her of course) so it was just a really bad situation.