Reality dictates our lives as being varied, complex and the corollary is that the grieving process is also complex and varied. The grief Demi feels is probably overwhelming, made all the more difficult by trying to sort out who it is you are grieving for at any given time. Demi has got to be patient with herself and you with her. I know this probably feels like an epidemic to your friend but in all probability it is not. Each death will solicit it's own set of circumstances through its completion.
Professional help is available.
How fortunate for Demi. Demi just needs to reach out. My advice to you, as her friend is give her a lot of space. You cannot imagine her pain and anguish. You have not walked in her shoes.