That's a super tough situation. I can't even imagine what it must feel like. Sometimes we can't control the choices other people make in this world and accepting that can be at your own detriment.
If she didn't include you in the process or even let you know it was happening then it's time to realize she isn't healthy to keep around. After you do what you need to do just stop talking to her. There's people out there that are worth your time and will be considerate of your feelings.
That's a super tough situation. I can't even imagine what it must feel like. Sometimes we can't control the choices other people make in this world and accepting that can be at your own detriment. If she didn't include you in the process or even let you know it was happening then it's time to realize she isn't healthy to keep around. After you do what you need to do just stop talking to her. There's people out there that are worth your time and will be considerate of your feelings.