women dont wear kilts.
Kilts are worn by men , kilts have to be a certain style and worn a certain way and traditionally no underwear is worn underneath. The material is usually tartan (plaid).
kilts should wrap round the waist and the length should go to mid knee, any shorter is wrong, any longer is wrong, wen u kneel on the ground it should be a fraction from the ground.
Women can wear tartan (plaid) skirts/dresses and i presume u know wot a skirt looks like, if they call it a kilt it will most certainly not be of the style a male wear it will simply be a plaid skirt.
So skirts and kilts are different.
Its up to the woman if she wants to wear underwear ;-p just like any woman has the choice to, its nothing to do with tradition.
Theres no 'rule' as women dont wear kilts so no comparison.
I hope this helps