Hello sorry your sister is going through this , this is definitely not a club she wants to be in but it does have the best support system and the best sisters in this club , so far I was told to drink these leaves called Soursop leaves , they say this fight cancer I take the leaves and soak them in hot water and drink it as a tea three times a day , I’ve also been told eating blueberries , a lot of green like my broccoli, kale , cauliflower, they say tomatoes, pomegranate, garlic, turmeric, grapes and noni, I have been eating some of these items but really doing a lot of the Soursop tea, I really hope this helps and i pray your sister is ok and the doctors doesn’t see anything in her MRI

I like to add something here--as a woman with breast cancer and also as a person whose sister has had breast cancer twice. To be supportive you can do all kinds of helpful practical things, but you don't need to come up with solutions or treatment plans. As your sister is finding her way in the medical world you are there as sounding board, back-up, and maybe even some fun distraction. It is so great that you care--that is enough and details will emerge. Best to you both.

I, like @mir123 will chime in with my own experience.
The best support I had was the people who helped me keep my life moving forward when I couldn’t. They helped with running errands, or going shopping, or driving me to appointments I couldn’t drive home from.
Depending on the treatment plan the “fighting foods” will be different. In my case losing 70 pounds during chemo from nausea, this meant whatever I could hold down was the best food. When my brother just lost his appetite, it was whatever he wanted to eat, because he never wanted to eat.
Since everyone in my family has or had cancer , I have heard on more than one occasion from an oncologist that anti-oxidants can be counterproductive during some treatments.
You could ask to sit in with a meeting with the cancer nutrition specialist, most oncologists offices have one.
I am so glad you are wanting to support your sister, she will need you. I loved every minute that I got to spend with my brother we would laugh and carry on, and I could forget about cancer for a while.
Do you live close to your sister?