Normally, I would say to look for "tall" or "extra tall" options in regular thigh highs, but your little lady is... little.
There is a sizing chart on most nylons online or in store. The important thing for you to look for is length. Most online ads for thigh highs are catering to the general masses, so while a pair MAY be long enough to go up to the crotch on your playmate... it is unlikely they will advertise in photographs this way. Which is why you are only seeing "top of thigh"/"proper use" images.