How much makeup should a 12 year old wear for school?

My little sister is growin up! And she wants to wear makeup!!! My parents are going to allow her to wear it, just not too much! I told her nothing lol but she got mad. Honestly, she needs something for her lips really bad! its like skin color :/ People made fun of her for her acne too. So my mom is really trying to stop that with letting her wear it. I dont know though. I am 13 almost 14 and I wear: light eye liner, eye shadow that stops at the crease, lip gloss, blush, mascara, and sometimes i wear concealer to cover up acne. I know I wear alot for my age but trust me, I needed it! :P Pleasee help! What can she wear that wont be too much for school. I was thinking from Un-noticable to tiny bit noticable. Thank you so much!