How do i tell my mom i need a bra?

ok so you probably heard of me asking this question, if not just go see it and im not re explayning the hole thing so just go and see my question (s) like this, so heres the prob now: me my mom and my lil brother went to walmart i was in the clothing section my mom picked up a AA bra or another size but it was a really small size and she said your gonna need this soon and i just went up to her and i said no ( just read my other qestion that says something like this one you will understand every thing) well that bra was to small for me and also my lil brother was there so .. but heres my question i need to tell her i need bras and for us to go bra shopping ( just us alone) and you already know i have 6 paded bras ( if not, just read my other question that the title is like this or almost the same you will understand every thing, like i said before..) so this is what im trying to ask: how do i tell my mom i need a bra (s) ( just read the question of mine that has the same title as this one or almost the same, like i said alot of times you will understand every thing) and i dont want any anwsers that say: just tell her straight up shes your mom. i dont want any anwsers like that or similar to that, so please give me good anwsers thank you!