To start the Casey Mall event you need the following:
Tiffany needs to have become immobile through the sandwich. 
Your debt needs to be $0
Fiona needs to be working at the Curio
Casey needs to be working at the lab
The Bookstore Clerk needs to have been fed the sandwich

Once all of these have been completed you will get a fun sequence at the mall that will lead to a plumped up Casey.

There is now a 1/6 chance to come across one of the two new girls when visiting the lab.
Once you have encountered one of them a new area will be accessable from the main lab menu.
You can choose one of two doors which each lead to one of the girls, the first one you choose will effect how the story plays out, though the beats are the same and it leads to the same outcomes. 
Just a simple matter of retrieving an item from either Vanessa or Aurora and then baking the appropriate item for each of them.
The option to make a "tainted" version of a baked good will only appear as long as you have at least one of those items baked. 
Once you reach the 4th weight stage that is the current end of the content, will be continued next month.