As they get older they don't need all the nutrition that a growing beardies does so she just might be slowing down. What I used to do to get beardies to eat greens is put the worms in the greens and the movement of worms in greens will get their attention. I have trained a beardie or two to eat greens this way, they accidentally eat one and realize they are yummy.

With yours I think its just a matter of age and/or maybe a brumation slow down period. 8 year old female beardies have stop producing eggs and their food intake probably drops with the less need for nutrition.