When Shannen first became diagnosed with cancer in 2015, Holly fell out with Shannen. Ironically, Shannon had a very close relationship with Holly and seemed to only had a problem with Alyssa, which is partly why she left the show.

Alyssa and Rose have been in a one sided feud (http://www.justjared.com/2020/04/06/alyssa-milano-explains-silence-on-allegations-against-biden-rose-mcgowan-goes-after-her/) on Rose's side since Harvey Weinstein has been exposed. Apparently, Alyssa was/is a Weinstein supporter. Rose was raped by Harvey while she was filming Phantoms.