So… uh… the game needs to check multiple values… I was FORCED to go to daily needs, which I had JUST left after buying Thick Pink Diapers, which triggered the message I need bigger diapers AFTER buying them. I knew I didn't have the money to buy diapers, yet the game wouldn't let me out of the loop until I went.
As for why I chose to request a specific diaper; I thought I had just bought bigger diapers. The mall calls them Pink Overnight Diapers, so, not being able to see the diapers I have at hand prior to that point (I had always let her change me) I had assumed that Thick Pink Diapers was different from Pink Overnight Diapers.
Game should check how much money you have, and if you have any diapers bigger than what you're tryin to wear…