DD1 got a present of a book by Bobbi Brown called Teenage Beauty when she was about 12. I thought it was great, and basically showed her how to wear makeup rather than have the make up wear her / have people see them rather than the makeup, iyswim. Probably the same book Liverpoolwelsh mentions. DD1 has really, really pale skin and after a few expensive mistakes settled on what suited her best - she took the book to heart but that is the kind of girl DD1 is.
I have let the DDs proceed at their own speed when it comes to matters like shaving, eyebrow plucking, wearing makeup, nail polish, etc. The only areas where I have butted my nose in is to insist they wash all the warpaint off nightly, and I have also told them how to avoid slicing themselves while shaving.
I think it's important to avoid having something like appearance come between parent and daughter because that magnifies the significance of appearance, which is probably not what most parents want. I also think it's important for a parent to acknowledge that their DD is in fact not a child any more and to encourage her to inch her way towards presenting herself as an adult. Girls need your blessing or else you are not really acknowledging the entirety of who they are or who they are becoming, and many feel the lack of this keenly.
A little makeup or even a lot of horribly badly applied makeup can give a girl a lot of confidence heading off to school. A girl who is not allowed to wear any can really stand out and it can put a dent in her confidence. But more important than the makeup itself is the fact that your mother is supporting you as you head out into the world during these years of change and growth; it's important to show your DD that you can empathise and understand her needs and that you do not fear the process of change. Try to embrace it all. It is going to happen with or without you wanting it.
Nothing should worry a parent more than the prospect of sending a girl out into the world in her late teens without the sophistication and confidence she will need in order to make a go of life either at university or living independently while working. You really have to accept and embrace and encourage your DDs' growth and constant change (and maybe do a lot of biting of the tongue) if you are to end up with a confident young woman.