How do I find food for lilly?
well in her case you have to go to all foods and buy a cooking book for 50$ (if i remember correctly) then in the book there are many recipies and three of them are those that lilly likes: chocolate chip cookies, brownies and banana bread.
in order to use it you have to go inventory, then pantry then "beginner's cookbook", after clicking it you will find all the recipies you can make, click on the one you want to make (for exhample brownies) and the game will tell you what ingredients you will need in order to prepare that "dish", you can buy them at all foods, after you have the ingredients click on prepare and the game will ask you how many, insert a number depending on how many ingredients you have (under the list of the ingredients you need the game will display which of them you have and how many) ah after you have "prepared" a dish at least once if you have Diane unlocked you can visit her and use the option "bulk shopping" in order to instantly obtain all the ingredients needed for said recipe (but you will still have to pay for them, obviously) ah if you prepare extra dishes you can go to inventory --> dishes --> and click on that dish and the game will give you the option to eat it (but the game mat also make you eat it automatically)
Ah also an advanced cookbook exhist but you need a higher weight stage (don't remember what though) while the begginner can be bought from the begginning.