Jill's mother knew she'd have to bring Jeff back. She also knew she wanted another daughter. She considered making her other daughter younger than Jeff but finally decided to make them both teenage. Dealing with a teenager was sometimes hard, but she was younger now, and she could handle it.
She carefully set up the Chronivac so that one of the babies would become male. This one would be Jeff and would remember everything. The other one would stay female. This one would become Jill. The Chronivac can do mentality changes, and she would have to be careful with Jill's memories. She could give Jill the memories of growing up as Jill, but they wouldn't be real memories.
Finally she decided on something a little different. Jill would just have Jeff's memories, but slightly changed to remember things happening to a girl instead of a boy. There was even a nice menu item, "substitution", for that. So basically Jill's memories would be real--since she is half of Jeff and they are Jeff's memories--they'd just be slightly different.
She also didn't want arguments about who's real, so she added 10% awareness to Jill--she'd remember what she remembered, yet at the same time know it wasn't real.
The whole procedure was less complicated than it sounds, and soon Jill's mother pointed the Chronivac at her stomach. It got bigger, she opened her legs and two babies magically slid out, and they changed from crying infants to toddlers, young children, older children, 13 year olds, and were soon back to their original age.
"Mom, I'm back!" said Jeff.
"Mom, I'm back," said Jill. "Wait a minute..."
"Are you okay, Jill?" asked her mother.
"Of course I am, I... Mom, Jeff over there... we're both the same person! He's really Jeff and I'm really Jeff... but I don't remember being Jeff. I remember being Jill but I know that I really wasn't!"
"But you are now," said her mother. "You need to remember being Jill if you're going to be Jill now."
"Yeah, Mom, but it's all so strange. I remember learning to put my bra on, things like that... but I know that it really didn't happen! And I remember things like my first day at school, I remember meeting everyone... but I remember doing it as Jill, and it only happened to Jeff."
"It's okay," said Jeff. "It really did happen to you, even if you don't quite remember it the way I do. Mom didn't want you to have completely false memories, just enough to be a girl. Do you really remember everything I do? Jill, what about, well, when I sneaked off with my friends into the theater to watch that R-rated movie."
Jill said, "Of course. We hid in the bathroom. Mom found out and grounded me, but later I wrote an essay about it for English Composition, and got an A...."
"We both did that," said Jeff. "We did that as one person. Mom hadn't split us yet. But tell me, Jill, where did you hide? Which bathroom?"
"In the girls' bathroom, of course," said Jill. "But that isn't right. It would have had to be the boys' bathroom. I only remember it as being the girls' bathroom because I remember girl versions of everything."
"Well," said their mother, "It looks like you're getting along fine. I'll leave you here to get to know each other better."