That really sucks. If you want to you could try talking to her about it, let her know the parts of the class that are difficult for you and also politely mention that you overheard her talking to other other teacher and it hurt your feelings. Of course, you don't have to do that, just whatever you feel comfortable with. You could also see if it's possible for you to get a different biology teacher, but that depends on your school. Best of luck, I hope your future teachers are nicer.