One moment Sarah was standing there, and then next moment she was gone.
"What happened to Sarah?" Fred asked.
"Who?" asked Fred's original mom, who was no longer his mom.
"Your daughter. She was standing right there just a moment ago," Fred said, pointing.
"We don't have a daughter. We've been thinking of adopting, but ..." said the other woman, who used to be Fred's original dad, but was now his mother, thanks to his most recent wish.
"I don't understand. What's going on?"
What was going on was that Fred's original parents were now a married lesbian couple who (because they were two women) weren't able to bear children, so in turn, their daughter Sarah was never born. This was a new reality, so they didn't remember Sarah, but thanks to one of Fred's wishes, they did remember him.