Aside from keeping your furniture in the dark, I don't think there is much to be done about this. The dye that is in the leather will have faded, as all colours fade over time and exposure to UV light. If someone is proposing re-applying dye, this cannot possibly bond as well to the leather as the original treatment, as the latter involved soaking in chemical baths and rinsing. Painting on a dye simply can't have the same permanence. Also, it may come off on clothes and legs.....
She could try moving the furniture round so that UV falls on more parts of it more equally, and the fading that is taking place is spread over more of the leather.