Do you, or can you get a calcium supplement like Calcium citrate, gluconate, or just plain tums. If yes, I would give her some of that.
One of the leading cause's of "sudden lethargic" behavior in waterfowl is reproductive problems.
Sorry to hear she's having problems. I would agree with @Weeg , that switching her to a balanced feed would be a good start.
Regarding her current state of health, could you answer these questions?
Did this lethargic type behavior appear over a few days, or suddenly? Could you post a few...