Ask your vet how much she should weigh, and check your bag to see what it says to feed for THAT weight (not what she weighs now). Then cut that amount back just a bit as, some bags tend to be overly generous with the amounts.

Be sure to use a real measuring cup, not a coffee can, butter tub, or things like that.

To keep her happier try doing several feedings through the day instead of just one big meal.

If that doesn't seem to be doing anything for her, you might want to have her thyroid checked just in case that may be contributing to the problem.