My friend's BFF hates me. What should I do?

Sounds complicated. If Emily was truly a good friend, she wouldn't change how she acts around you when Lisa is present. She would tell Lisa to be nice and include you. Real friends are always there for each other & have each others backs. However, it sounds like she [[Emily]] is following what Lisa wants. I think you should take her aside and tell her how you feel. It's the only real way you can resolve it. Also try finding other people to hang with when Lisa is there. :)