At the end, Em discovered that there are so many different realities, and after that blackmail chaos she left the current reality (which is not her). Em visits various realities, which have different different outcomes but most of them are dark. Then, she visits a reality where the people never leave the room. She breaks the car glass, which makes everyone check outside, and gets a chance to tranquilize her (this reality's Em) with some ketamine that she had taken from Beth. But she became conscious again, and a second fight ensued in the bathroom. She killed her or nearly killed her (we can't be sure, because in the morning she disappeared).
At the end, Kevin gives a ring to Em. She finds this ring in the bathroom, and now Em has two rings. After that, Kevin receives a call from another Em. Now this part is left for open interpretation, which Em called Kevin. She may be the same Em who nearly died in the bathroom, or she could be another Em.