Jeff thought "Umm.... Just make it so she can't get in here!" So going to his mother's profile the quickest thing he saw that could think of was...
His mother was approaching Jeff's room, knock on the door, and ask for some help getting groceries and then got a tingling in her chest as her breasts started to rapidly grow and burst out of her shirt. Off balance she fell forward for a second, and found it almost impossible to keep herself balanced.
"Jeff! Could you come out and help me with my... Whatever's going on!?!" Jeff's mom exclaimed.
Jeff could only think "Fuck, this thing's got my dick thinking. Of course that'd stop her from opening the door, but it's only going to make her keep asking questions... Maybe?"
Jeff's mother was flabbergasted, what was Jeff doing? As she tried lifting herself up she found it getting easier as her old muscles started to feel stronger... and then the weight itself seemed to be getting lighter. She was able to get herself up and open Jeff's door. Jeff was scared to think of what his mom would do when she figured out what he did to her. The current teenager looking mother with merely giant breasts was now in Jeff's room, but her regression started accelerating as her hips and chest shrank back into her body as her puberty undid itself. The tween turning into child was swimming in her clothes as she continually shrunk further and further. Her hair getting shorter and thinner and even her teeth starting to retreat into her gums. The little baby collapsed into a pile of clothes and started crying unsure and confused about what was going on.
Jeff thought to himself "...Alright... Mom's a baby... and she'll just have to continue to be a baby till I can figure out a good way to explain everything... or maybe mess with her memories or something... But how the heck can I keep this a secret?"