This may sound strange at first, but it is a fairly uncommon if not rare condition.. I have it and had since I was a child and injured myself doing gymnastics, it can happen without injury too.
It is called meralgia parasthetica, and involves numbness on the outer/thighs, legs/hip areas and stems from a nerve being pinched on one or both sides of the hipbone/groin area. It's a subtle thing if there is no pain involved, but the brain knows it shouldn't be numb and it just feels wrong or overly constricting. Sometimes there is pain (mild to very severe) involved but not often unless the person is overweight or has pregnancy or wears heavy belts like workbelts. I didn't know what mine was til I was an adult and became pregnant.
Mom could never understand why I hated pants, especially jeans and I wore skirts all my life. I actually made her buy me a garter belt in high school ( a nice matronly sturdy one mind you, not a sexy one haha!!) because I couldn't STAND the feeling of nylons across my thighs/hips.
I know it's a stretch but try to ask her WHY they feel weird, ask if she gets pins & needles on her upper legs or if they don't feel the same as the rest of her leg in those areas I mentioned. Or try to find out why she doesn't want the waist constriction. If it is just a "I don't like it" kind of thing, then don't worry, but maybe mention it at your next doctor's appointment just in case. I hate to worry you unnecessarily but if it such an obscure little condition but affected me my whole life. It's much more well known now than in the early 70s.
If there is no medical or sensory issue and is just her not liking them, what about longer skirts with drawstring waists? Those can be very comfortable.
I am 41 and STILL wear only skirts , usually to lower calf almost ankle length, and never wear tights or nylons :)
I hate to say it mom, but maybe she just hates the feeling. So long as she isn't complaining about her legs being cold then maybe just let her be comfy.