GAW – I have heard of such an opinion, although I wasn’t sure who said it.
Rav Ellinson quotes the Minchas Yitzchak who speaks very strongly against girls wearing pants in order to ski.
L’maaseh the opinions allowing pants in general or just for skiing have not been accepted l’halacha. And it certainly would be hypocritical for someone to rely on Rav Vosner for this if she doesn’t go by him in general.
My point was that if pants are not technically assur, then I could see there being room to say that if someone’s skirt goes above her knees, it’s not a problem.
Additionally, even according to the majority opinion (which is what the oilam holds by today) that pants are completely assur, the question would be which part of the pants are assur. I left out part of the Yaskil Avdi; the next words were “to the very top” which could leave room to say that the part by the knees is not a problem.
DISCLAIMER: This is all my own conjectures and should not be applied by anyone l’maaseh!