We all know that Vermouth and Sherry have some sort of antipathy between them. Vermouth hating Sherry, Sherry fearing Vermouth. Why? As Vermouth said in Chapter 818, "She's the only one that can't be allowed to exist in this world." For saying that, it means she has some sort of hatred towards Shiho.
My Theory
So, what do you think? What are your theories?