Question about scenes leading to Daisy's suicide.

Can anyone please explain to me when Daisy kills herself and Susanna is back in the hospital and crying in her bed and Valerie enters. Susanna says something, "a decent person would have done something like that to shut her up". What does she mean? and who she refers to when she says that? And when she says Lisa thinks it's a gift that it lets u see things. What does she mean by that?
Would appreciate it thanks.