She posted it as "friends only" and tagged her family members. The person who tweeted it saw it and assumed that it was showing up because she is a subscriber of Randi's public posts, though in reality it wasn't public and she saw it through a friend connection with one of Randi's sisters. She tweeted the image based on that assumption. Randi saw it, was surprised, and then discovered how it happened (because Randi knows how privacy controls work quite well). They communicated on Twitter and realized the misunderstanding. The end.