I did the same with the food ("diet" kibble, same measurements). The biggest thing was getting her to move. I had to dedicate time after work to play with her until she was a little winded. I did minimum of 4 days a week. And it took some time. I adopted her in 2021, so it took a good 3 years to get her down. The smaller they get, the easier it gets because they start doing extra stuff on their own. Like, once she got energy, she would do "zoomies." First just here and there, and soon she was doing laps at night just cause she could. When she lost enough to get to that point (I want to say that was around 18 or 17), she started to lose more. The first year I got her to the 18/17 range, but the by the second year, she was one pound from her goal.