LMrob... what are your weather temps and such ? from the photo she is a tad hairy. I also use flax seed to help some of the horses shed. I buy it at Walmart .
be careful with the Vit A , they can get to much . I also will disolve a vit E, b complex and C and pour it over the pelleted feed.
Also check your pasture, there could be weeds with the little fine hairy stickers and that will cause them it itch.
If the hair does not shed, I would have the Vet run a blood panel to check for cushings or any other illness. Hope she sheds soon.