It’s symbolic in that she was still naive. She’s an old woman with a child’s haircut symbolizing her choices are childish. All those years and yet she thinks she can “give them a happy ending” it shows she grew, but not enough.

I personally always thought the actions were more motivated by jealousy than actual mistaken identity. That as a young girl she thought accusing Robbie would get him taken away from her sister but not ruin his life so thoroughly.