Hi av,
The best she can do is try on lots of stuff, it all fits a little different. My feet are a Women's size 7B, I have Alpinestars Tech 5, size 6...which are a bit roomy on me - I put in some 1/2" thick "Airpro" insole inserts and wear heavy wool kneehigh socks and they're just fine. The buckles are awful tho, have broken and replaced the middle one on both boots and they're difficult to work. They're maybe 5 years old now. They hit about an inch and a half below my knee.
My Kneeguards and elbow guards are both Kid's sizes, otherwise I just wear men's small everything else...Fox chestprotector, Thor pants. I'm a bit over 5'2" and small. Haven't tried any of the women's gear, which they do make some now, but was never an issue with my carpenter's-dream body...
Good luck!
Susan
BBR230