If Emma was threatening your daughter and making her afraid, hitting her, making fun of her, making her cry etc, that to me is more bullying.
I would tell your daughter Emma is mean and she should ignore her and play with other girls. Teach her how to say, "Emma's not your boss, let's play!" Encourage her to tell the teacher when she has been "turned away" by the "group" and her feelings are hurt. I would also let the teacher know what may be happening, and have her assist in making sure your daughter (or any other child for that matter) is not alienated at school. I don't see why a teacher couldn't "assign" play groups a couple of times during activities or even recess. She should also call a class meeting in which she explains to kids what type of mean behavior (excluding each other) is not allowed. My daughter went to a Christian K4 with strict bully policies, and this certainly would not have gone unchecked in any of the grades in class or on the playground.
If things continue or get worse, I would have a little talk with some parents, including Emma's in a "let's all solve this together" type of way, not an accusatory way, and keep on it. Good for you for realizing it may be embellished, but be prepared.