She wears size 5 pants and is 5'2" and around 120-125 lbs but leggings are in s, m, l, etc because women's clothes have to be overly-complicated to buy for some reason. I know she'll either be a small or medium, but I'm not sure which and I don't know anything about buying leggings (like if you should buy bigger since they are so tight).
Here are the measurements of the leggings:
Waist: Small = 26", Medium = 27.5"
Hip: Small = 32", Medium = 33.5"
Inseam: Small = 28.5", Medium = 29"
Most Helpful Girl
small is usually from 2-4 and med is 4-6.
since every store/brand is different, i look for the sizing chart from one of the pants to see the measurements and compare them with the leggings.1