[Ellie May]

First, did the vet do bloodwork?
If nothing has changed and she was doing well on the amount of food you give them, then there may be a medical problem involved.

If that has been ruled out, you can try a senior dog food or one meant for weight loss or you can replace some of her normal food with certain vegetables to make her feel full. If that doesn't work, she will likely need a prescription weight loss diet.