I'm so sorry to hear about this! :( I hope everything goes smoothly during her operation. Depending what you have available in terms of crystals/stone, and/or places to obtain them, I can write out a list of stones said to aid cancer, kidneys, and post-operation stuff. You can make an elixir with the crystals and have her drink it daily until she's all better. Most crystal-infused elixirs are safe to drink; if there were to be some caution surrounding a particular one, I will let you know as there are still ways to use it. I will type these up in the morning, as I am sitting here in the dark and can't read my books properly.
If you can't be open about your practices, you can still use the stones to help heal her, or incorporate them into a distant-healing spell.
How open can you be about using magick/alternative healing to help her?