My daughter is a 'regular' size ten so I ordered her a 10 in these leggings, but they were WAY too small.  I think they were more like a size 6 or 8.  I returned them and did not attempt to order again since sizing seemed tricky.  Might be better to buy this type of product from a big box store where she can try them on.  They were very cute, though!  Sizing just seems off.