I suspect that your sister has been left traumatised by what happened.
She might have kept it bottled up throughout most of her life, but it sounds like she needs help now.
You've made it clear that you don't want to discuss it with her. That's your right. However, could you suggest kindly to her that she seeks counselling, as she really sounds like she needs to talk this through with someone.
*International Plastic Bag Free Day* tomorrow July 3rd
Only 50% of middle age adult manage more than 1 brisk 10 min walk a month.


