As long as Gollum continues to eat and doesn't start rapidly losing weight it's all good.
A little extra weight is a good thing for a kidney cat as they often lose weight and it then becomes quite hard to gain it back to get them back to a healthy weight.
If you can get her on mostly canned food with little to no dry food that would be even better for her kidneys as that will provide some extra moisture and not dehydrate her like the dry food will.