Something to consider in your wife's case is whether the offensive agent can be a single spot of light, the general intensity of light in the whole scene, or both. Is rod vision, cone vision, or both most involved?
I fear that your LED solution might actually aggravate the condition, as the LED's would likely be perceived as individual spots of light against a more uniform changing background of light. That situation might be made even worse, if the LED's were off axis while the viewed scene was on axis. (Rods are more sensitive to flicker detection than cones). Thus, changes in the average light intensity might be reduced, but the perception of flicker might be increased.
As an alternative, you might consider using an LCD screen as a filter. Voltage applied to the screen could cause uniform darkening and lightening. Thus, when viewing a scene with variable light intensity, the extremes of variation might be reduced with such a filter.
John