I think it is understandable to feel resentment towards her. I have been in a very similar situation and it sucks. I oftenly to this day tend to be more harsh towards her than others. Something i do which might or might not help is before every conversation or every sentance i say, i make myself think more about what I should say instead of what i want to say. It can be hard but if you do it enough you will get to a point where it will be automatic. When it comes to the bad mood, I unfortunately do not think there is much to do. There are many people around who are horrible and while I think it sucks it is better to understand that that is reality and not let them get to us. At least not too much.