Thanks a lot for writing in today. It sounds like you're facing some serious social bullying, and it's good that you're reaching out for help.
It sounds like your friend is trying to keep things under the table by doing everything behind your back and without saying anything to your face, and one option for you is to bring it out into the light.
It's really difficult when friends bully friends, but the good news is that friends can talk to each other. And you can talk to Emma about what she's doing, and tell her that the way she's disrespecting you really hurts your feelings. You won't just be helping yourself by trying to stop the bullying, you'll also be helping Emma to become a better friend. It doesn't need to be a big, forceful stand, but just tell her that her behavior is really hurting you, and that friends shouldn't treat each other this way.
If she won't listen to you, and she wants to continue this disrespectful behavior, then you could try gathering more of your friends to talk about it. This is where social bullying can be stopped, when a group of people commit to working together to be better friends. And if you all get together to acknowledge that you've been mistreating each other, then you'll all be happier in the end.
We hope that helps, and if you ever need additional help, just get in touch. We're here to support you, and we wish you all the best.