My feet are actually not that small, despite me being only 5'1" and 105 lbs. I'm a street shoe size 7 and measure a 23/23.5 on a Brannock device. I am in 22/22.5 boots though, for other fit reasons. Definitely get her to a fitter. Like someone else said, her having such small feet may or may not be a good thing this late in the season. Either places won't have that size b/c they sold the few pairs they had or they'll have some left b/c it's a less common size. Junior race boots may be another option for. Dieter at Alpina (near Jack Frost) carries Head junior race boots. Not sure what he has in 21.5 outside junior ski boots?
As far as skis, at her size she could definitely get away with junior skis (I've had junior skis before and currently have a pair of junior slalom skis) but she doesn't have to get junior skis. There are plenty of shorter women's skis too. I've owned women's skis from 142-149 cm. Just make sure if she does get junior skis that they're wood core and not foam core. Some kids skis are foam core so beware.