Professors what do you think?

She ( my lecturer ) ignores us students , never looks us in the eyes as she speaks to us and she is tough on us .      
Either way, I admire her as she is very mart and knowledgable .      
I was standing outside my classroom, she passed by me twice and smiled at me but i was super nervous coz i didnt expect that so i just stood there with my poker face .      
Yesterday when i saw her again, she stared at me across the hallway and when i was about to say " hello Mrs." , she looked at the other way and put a tight- lipped smile . (Evil one i guess..)      

What the hell does that mean ? Am I in trouble ?