Those ruffians, the Gods, shan't have it all their own way, – her notion being that the Gods, who never lost a chance of hurting, thwarting and spoiling human lives were seriously put out if, all the same, you behaved like a lady. That phase came directly after Sylvia's death – that horrible affair. (4.69)
Clarissa witnessed her own sister being crushed by a tree – an accident that was apparently her father’s fault. Like Septimus’ reaction to the loss of Evans, Clarissa moves on and behaves "properly" (meaning stoically) in the face of trauma. Clearly that doesn’t help anything.