In my opinion, teaching young women to understand their motivation for things is more important than teaching "this is an acceptable skirt length".
Both the woman in the niqab and the woman in the mini skirt could be wearing their garments to appeal to a misogynistic ideal set by our patriarchal society. It just comes in different forms.
Understanding that wearing whatever we think we want to wear has to come with internal analysis of all the factors that contribute to those choices.
It suits society for us to be both Madonna or the Whore, and whichever we choose is wrong.
There is nothing inherently wrong with dressing completely modestly, or dressing completely the opposite... But thinking that it's all down to an "independent" decision based on feminist free will is simple incorrect.
There's nothing wrong with wanting to be attractive to men... But are we dressing in a way that contributes to the commodifying of women's bodies?
Or are we dressing this way because the sun feels good on our bodies and we like the way we look, independent of outside influences.
And don't forget, religion is the basis of most of the oppression of women. It has been used to keep us in a very small box while men have had their way in the world, doing appalling things hidden behind the face of righteousness. Is adhering to modestly laws set out by these men really our choice? When we face shunning and shaming from our communities?
There is so much hypocrisy, victim blaming, slut shaming around women who wear less clothing... And then there's mocking of those who don't. They are prudes and boring and men will say that is what they want, whilst watching porn of the opposite.
Women literally can't win. So teaching daughters all of the context surrounding why we may choose to wear what we do, is really important. As is the attitude of "fuck it".
But it's an incredibly complex topic.