Should I bother being nice to my lecturer?

The head of my department in university is the most ignorant person I have ever met. She completely ignores us on the corridor and is very rude to us when lecturing in cl. I feel as though I have to be nice to her in order to get a good grade as whenever someone questions her she looks far from impressed. She completely belittles us in front of her peers and in seminars she orders us to move seats etc to make way for more 'important' people (if they had of got there in time they would have got a good seat!). The problem is, she has got a very high rank in her field so she doesn't have to answer to anyone The field of work that i'm training for in my masters involves a lot of theraputic work with various people. What I don't understand is how someone as rude and unprofessional can have a job in something like that which requires you to be friendly and approachable! What should I do?