Should a preteen girl wear a miniskirt with nothing under her skirt?

No please. Underwear is very important for higiene and comfort. The friccion of pants with your intimate parts can cause irritation and you might get an infection. Besides, if you have an accident, for example you tore you pants for mistake you wouldn't like to nude in front of people. So girls please wear your underwear. If you don't like panties you can wear g-strings.

Thanks!!