Opposite to the idea of just monitoring kidney function until the point of dialysis, herbs and diet can go a long way in protecting, stabilizing, and improving kidney function. There are multiple herbs that are helpful. One of them is milk thistle.
Most people who have heard of milk thistle know it as a great herb for supporting and protecting the liver, but it does the same for the kidney also. Studies have shown milk thistle to attenuate kidney damage in mouse models. Mice were separated into two groups, one did not receive any milk thistle, while the other did. The milk thistle was given prior to intentional kidney damage. The group who took milk thistle suffered less kidney damage than the group without milk thistle. This word 'attenuate' can be seen as 'prevent.' But milk thistle can also help support the kidneys even when they are already damaged. You can find studies about milk thistle and kidney function through pubmed.gov. Type "milk thistle, kidney" or "milk thistle, renal" in the search bar, and they will appear.
Avoiding herbal diuretics and foods that are notable diuretics, like watermelon, are also important to avoid making a damaged kidney work harder. Moderating protein intake, especially animal protein, is important in order to avoid kidney damage.
Taking milk thistle in proper dosages daily, along with a diet that does not cause further harm to the kidney, can help preserve kidney function.