I think your sister-in-law's behavior and reaction are normal now. After all, when a stranger comes to a new family, everything doesn't adapt. She is more wary of the new members of her family, not knowing their temper and being afraid to talk too much. This is all true, but as long as her sister-in-law and her sister-in-law treat others with a sincere heart and treat each other as bosom friends, they will meet each other over time, and one day you will, too.