Dogs can back off of food once satisfied. Mine are bottomless pits, but they can. I am not that familiar with that food, but will look into it. I have a feeling she is backing off because she feels constipated. You can cut back on how much you feed. Remember they go through changes in how much they need.. Sometimes adding a little meat ( without bone if you add kibble) like raw chicken breast ( no bone) or even chicken livers might help.
As far as constipation- take out a little of the food and use warm water to soak. My dogs also like broccoli- or asparagus tips.. ( raw of course- or steamed but I use the left over water to soak the food when I steam the veggies) .