I have one sister a year younger than me. We were very close our entire lives, we would have an argument now and then but nothing serious until last year. We had quite a nasty argument and did not talk for over a year. In fact, had I not talked to her first we still would not be talking. The only reason I did call her was to put my 87 year old mother at ease over the situation. My sister said some really bad things to me that honestly, I won't forget so I will probably never get past that.
So while I did make peace, I don't really see anything going back to the relationship we once shared. I will not be making any big efforts to see her and I know from the past that if don't bother talking to her, she won't bother talking to me.
I figure at least when my mom goes hopefully we will be able to at least be civil to each other until the funeral is over. The folks made her the executor over their estate so hopefully she does not do anything really wacky. My sister has always had a way of becoming a bit pious about religion and sometimes she does some goofy stuff because of it, or in the name of it. I never discount that as a wildcard.