Let her wear some light makeup and show her how to do it - some mascara, blush and lip gloss would be fine. She'll probably be so thrilled with that she'll forget about the padded bras (which is pretty inappropriate) for awhile.
They look up to us and others. It goes along with society and peer pressure.
they want to look like the girls on tv and so they change themselves to make them feel better about themselves
You could tell her that she's pretty
and she doesn't need to change herself,
if the boy really liked her back then he wouldn't
even mind if she doesn't wear makeup.
Well, for one being grown up looks a hell of a lot better than having to do everything that your parents say and having to ask for permission every time you want to change something you don't like about yourself (especially when your parents disagree)
My opinion is that the best solution to these kinds of situations is a frank talk on the reality of getting older, of the exact reasons for her rules and prohibitions (because I said so is not a valid reason), and a sense of independence and trust.
EDIT: Just for instance, if you felt that you needed to change yourself for some reason (say you want to be more athletic and run every day, that is a common one for a lot of people), and your husband/significant other not only told you that you don't have to run to feel better about yourself, but that anyone who might like you already does, and that any change you make won't change anyone's opinion of you. To top it off, the explicitly make it impossible for you to run.
Is that really the message that you want to send across?
"If they really liked you, they wouldn't care if you wore makeup" translates to "They don't like you, and they never will" Statements like that are not going to make a teen or preteen feel better about themselves...