How do I deal with a dramatic, narcissistic co-worker in a very small work place?

I work in a Veterinary Clinic as a Veterinary Nurse. It is a very small clinic with 8 staff, it is only the size of a small house. It is fine when other collegues are around but very difficult when we are working alone together, I have tried very hard but anything I do she claims I am being rude to he. We have a difference of opinion and when I walked way and would not enter into conflict with her she started yelling at me and going psyco. She loves to be the center of attention and will use drama for this. I have always dislliked her as a person but have always been polite. She was born with a silver spoon in her mouth and is used to geting her way. So I am wanting help with any coping mechanisms or strategies to help work with her. I am only 24 and have never being in this situation before. I have twice the amount of experience as her and we are equals in position but she really likes to bark orders at me (no please or anything) and feels she is much higher and better than me as she started working there a few months before me. I have tried to only speak when it is to do with work and she sniches to the boss that I am being rude, I have tried to be polite but appartenly she dislikes the way I am speaking with her. To be honest my boss has always shown favouritism towards her according to everyone as she looks after his young son sometimes. So he thinks I am getting worked up for no reason when actually this is me acting completely neutral, if I was worked up she would have my knuckle marks in her face. I now cannot approach him about anything she does incorrect at the clinic or when she is nasty as he said I am being petty. Any help would be appreciated. I think this is all bull to be honest I'm just there to work and she should just shut her mouth and work