I think you need to realize her concerns are entirely valid. Everything could go great and you could both have 1 working kidney then live long lives after. You could die on the table. You could give him your kidney and then 10 years from now your remaining one has an issue and then your on dialysis. etc. Your daughter is not wrong to be scared/concerned. You are not wrong to want to help your friend. Both of you have valid feelings about this. You just need to talk about them. In person preferably. Not over an email. Explain to her why doing this is so important to you. Make plans for what happens if the worst outcome happens. You need to seriously ask yourself: “Will my family be okay if I die on the table?” before you go do it. Because if the answer is no and you haven’t considered that yet it’s something you need to think about. I hope everything goes well and you help your friend and both of you are fine. But I also hope you go into this understanding your daughters concerns, and being fully aware of all the risks.