I wonder if she can wear things that have 5% or less lyrca/elastane/spandex. I don't have a reaction to them, but I tend to avoid synthetics for sensory reasons. Finding cotton or rayon yoga pants with small amount of a synthetic stretchy fiber in a budget brand isn't hard. But yeah, it'd be damn near impossible to find budget or mid-range yoga pants in 100% natural fibers. I'm honestly not certain something that needs to be that stretchy could be done 100% natural at any price point. (Please someone prove me wrong on the last. I'm a bit of nerd and love knowing about fibers and fabrics.)