got the same problem, did you figure out how to continue?
You have to do 100 of her ramen store content. lock in obedient or unobedient level for her and talk to her about a couple of the things revealed during the quests. And pay very careful attention to the responses. if she is agreeing to help you with a job then you are messing up spending time focused on her, and should be working on Himawari.
There IS currently a bug in the game where Himawari can cause a softlock if you let the scene play out where she finds out what she has been taste testing before you have done it 3x. If this happens, you game is softlocked and you cannot get to the modelling.
Until you have done the taste testing 3x and completed that quest. either do not lock in love or hatred route, or do not pass a night by sleeping and let that scene happen. Use dreams instead to pass the night.