Should I continue with her diet?

First photo is now and second is before december. I am not sure if I should continue with her diet. (Her being overweight was due to her telling my sister I did not give her lunch nor dinner and my sister believing her)

She have always had a chunky form but it got to the point where she had issues walking and breathing.

Shes way better with mobility and breathing now. Been feeding her half a cup of Purina One Plus healthy weight kibble at breakfast and another half a cup at dinner.

Should I go back to the normal feed? Should I continue with her current regime? Vet just told me to lower her weight and left btw.