How can you ask your mom to wear a bra?

One way is to point out some Bras on sale at a store, that's what I did

well when it is time for you to start preparing for a bra tell your mom that you would like to get a training bra if she is not comfortable with you having a real bra yet. after a month or two ask when you could maybe get a real bra. if you are shy to talk to your mom about things like that ask her on the phone either in a text or a call. if she is still not comfortable with it keep trying every month until she is if it has been 5 months you need to sit down with her and make her explain and help her understand that you are ready for a real bra.