I'm just shy of 5'2, was around 115-120lbs (packed on a little recently!
), and wore a fitted size XS in Scorpion gear at the time. They have a pair of pants called the Savannah that is quite low-rise and fitted and okay for my 28 inch inseam. I have a straight figure so I usually wear a size smaller in waist than people the same weight/height as me, so it would probably fit her comfortably.
Aside from that, I've found I am the smallest size in ready-to-wear gear made in the US/Canada like Olympia, Joe Rocket, Tourmaster, Icon, etc. and even then, sometimes the smallest is to big.
BMW I've tried size 36 and it is too big on me. Size 34 would be perfect so at least for some pieces, it still might be too big for her. Rev'It fits small (except for some more ADV pieces - Revzilla reviews are great, btw) but Dianese fits really small! It's expensive and not as readily available here but might be one option.
You should have her go to a store and try things on so you get a better idea of how each brand fits and how SHE likes things to fit.
Good luck! Finding gear can be difficult for female riders but even more so for really petite girls. Manufacturers have been good in adding some plus size gear but I wish they would do the same on the other end of the spectrum!