> Her oncologist didn't like the idea because there is also lots of research that says it spurs growth in tumors.

To be fair, if that's the effect you're going for it doesn't seem like the best option. If you want something to promote oxidative stress, take something like pawpaw supplements or a drug like metformin.

Tumors need more energy than normal cells, and oxidative stress interferes with the ability of your mitochondria to produce energy. So yeah, it makes intuitive sense that antioxidants are not what you'd want for cancer. Although as you mentioned, these systems are pretty complicated and there are a lot of chemicals that can act as antioxidants in some circumstances and oxidative agents in others.