Well, that's a good question that I've been fumbling over myself. Lilian is not the girl she used to be, so normal Pull-Ups won't fit her anymore, and she'll likely need something more custom. I was thinking that an accident should occur at some point, followed by Amelia having some time back at the lab to work with the objects she has there. From the things she has, she could devise a way to create Pull-Ups (and later diapers) in a small-scale sort of manufacturing setup, which would give her customization over size and design, so long as she has the right materials. She is constantly learning, so there's no reason for her to not be able to do that, especially since she has liberties and control over how Dr. Parks bank account is used.
So it'd start with Pull-Ups, and then eventually cascade out into diapers again as time went on. The Pull-Ups would be designed in studio from Angie, who by then will have access and knowledge of driving or maybe build a transport drone or something to make it happen (who knows?), which could also lead into her building different things she may want to use on/with Lil (such as furniture, toys, "toys" and the like.
Lets hear your idea.