[Maximo]

That's good that she is an adult and that your vet didn't seem overly concerned about her weight.

Is she spayed? Intact females and males tend to be thinner.

Are her rib bones visible? You should be able to feel them easily, but not see them.

Have you tried different brands of food? As long as she is healthy, you could try a food that is denser is calories. Compare the calories per cup of different foods.

I would also free feed, meaning leaving food in her bowl all day. Be sure to change the food that she has not eaten at least once daily.

I'm sure there will more suggestions from other members shortly.