The habit of careful saving, even when you are wealthy is an important life skill. Otherwise kids get to age 20 feeling entitled and disappointed they cannot afford a 52 face palette.
Or she can learn that you do your research and decide what is worth buying, and what is not. Buying the cheapest item is not always the best value. With makeup, you need to see what is best for your skin and for you. I have a lot of what would be considered expensive makeup, but it lasts a lot longer, stays on a lot longer and uses a lot less than many of the cheap products I have tried.
If a young girl is interested in makeup, that doesn't mean she's going to grow up to be an anti-feminist or a tramp, it just means she likes makeup. I'm 41, a teacher, a single parent, live on a farm, about as far removed from 'sexy' as you could imagine, but I spent some time this afternoon trying to practice a makeup look I'd seen on youtube. Because I like makeup, amongst the other 20,000 things that I also like. I don't do it for anyone other than myself.
It is far better to teach young people how to apply makeup properly for the best effects, how to take care of their skin, and how to select the best products for themselves, rather than a blanket ban on it. A nine year old learning how to apply some basic makeup appropriately is not a big deal, and better than then getting hold of some two dollar glittery rubbish and putting it in their eyes. If she's already interested in makeup, then her parents saying 'no' is not going to suddenly make her stop wanting to use it.