My mom is now worried about her 70% kidney function and cysts. The doctor said the cysts are small not to worry. How can I calm her?

You don't say how old your mom is, or if it's both kidneys that are at 70% or just one. I know that the older a person gets the more they seem to obsess about their bodily functions, so maybe she's worried that things may not work as good as they used to. The fact is she has two kidneys, and people live just find without one of them. You might remind her of that. When you get old, nothing works like it used to, everything seems like it's on the fritz so maybe she just needs to worry about something. Bummer.