
What is her actual weight like. Can you feel her last ribs easily and her backbone fairly well?
If you can't then she is actually overweight and it could be now that she has stopped growing she doesn't need as much food as you think, and eats the delicacies when you add them but not really hungry or needing what you give her.
I would cut her food by a quarter and not add any treats to it at all, and none during the day either. Put her food down and take up if she doesn't eat in in a few minutes. when she realises nothing else will be forthcoming she will look forward to her reduced meals and clear them with gusto. Dogs can go several days without food without coming to harm, as long as they are drinking plenty.
One of mine was one of those determined to stay ultra slim and when in season or just after might only eat 3 days out of seven. Now as a spayed senior I have to watch her like a hawk, as she now will eat for all she's worth.