With the weight loss, there is likely loss of muscle mass as well and this will cause the serum creatinine to fall without any improvement in her kidney function. I cannot make a specific diagnosis based on the information that you present. The fact that she is again making urine makes it easier to do her dialysis treatments because less fluid will need to be removed. I do not know what the cancer has to do with her kidney disease but it could be related somehow.
I suggest that you consult with her dietitian at the dialysis unit for suggestions about how to gain weight and improve muscle mass.
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