Most teenage girls like to experiment with their makeup to find the look which suits them and hide their flaws. If you want to cover red spots you should apply concealer in a green shade first and then continue with one similar to your complexion.
Only a dermatologist can give you advice on how
to deal with skin problems.
At this age you don’t need to use a lot of cosmetics, you are young and beautiful anyway.
For this make up look I used Garnier BB cream instead of a foundation. I chose neutral eyeshadows from an Avon palette.
For her brown/green eyes I chose brown eye pencil, as I don’t think black would be suitable. In case she had blue eyes, grey eye pencil would be another discreet choice.
On the lips I put a purple lip liner and pink lip gloss from Avon.
I used bronze pearls for blush and brown/black mascara from the same brand.