Step 1: Let her know that she is beautiful
Tell your daughter that she is beautiful from a young age. She will believe it, which will increase her confidence in herself.
Step 2: Allow make-up - but just a bit
Even when your daughter is asking for your permission to wear make-up, remind her of how beautiful she is and that she does not need to wear make-up. She may feel pressured to do so since her friends are also wearing it. Allow her to use just a little - a basic mascara and transparent lip gloss should be enough.
Step 3: Stay firm when choosing her wardrobe
Since you purchase all her clothes, her appearance is your responsibility. Choose appropriate clothing that do not show unnecessary skin. Low-cleavage and belly-showing shirts should be avoided. Likewise, skirts and shorts should be long enough to cover any inappropriate parts. Do not encourage her to wear clothes with writing over the breast area or over the buttocks. If your daughter picks something that you consider inappropriate to wear, present her a more suitable alternative.
Step 4: All her friends have it
If you deem the item in question to be inappropriate, then tell her no. She will not understand that her friends will change throughout her life. Still, let her know firmly that your standards are not to be compromised.