Have a good look at her feathers, any other signs of moult? Ha ve a good look at hte scales, any evidence of a greyish subvstance under the scale? You can paint her legs with
benzyl benzoate available from the chemist, very effective if you suspect SLM, Ivermectin is another good one that vets recommend. Meanwhile you could smother her legs with vaseline just in case. If it is scaly leg mite and you catch it early it is quite easy to sort out.
You will have to check all the other birds and clean henhouses thouroughly to prevent other birds becoming infested.