If Mom's corruption is at least 3 and you go swimming in the pool with the Cheerleader (weekend afternoon event), you can get an option to "Tease" her.
Then if your corruption is at least 4, during the conversation you will have an option to agree with her that you should try a bikini, with the option "A bikini would be fun".
Once you have passed that, you can create a bikini for Mom at your sewing machine.
