firstly, we cannot say ayahuasca can or cannot cure cancer. None of you know this, period. there is enough studies that do show anti tumor effects of peganum harmala extracts etc, but to extrapolate from that statements on ayahuasca curing or not curing cancer makes little sense.
That said, I dont think ayahuasca is going to make it any worse.
If it was me, I would get on a seriously clean diet asap, and start on high doses of cannabis juice or oil daily. Cleaning up lifestyle factors is not going to work against a person, even if it does not work as a cure..might as well try.
Beyond that, I wish you/your friend the best.
If you want alternative medical advice(for treatments like herbal regimes, ayahuasca etc) you should probly get your friend to see a competent naturopathic physician or herbalist etc. There is an american herbalist guild that has strict requirements of years of real clinical herbalist training to be a member etc, that can help you find such people in your area if that is of interest. You should really seek out these people for more information as they are qualified to give such information. Im not big on these kinds of guilds etc that over regulate stuff but in this case it is probly useful to help avoid the overnight internet certificate people who dont have real expeirence etc...
Turkey tail mushrooms are really big as a cancer treatment and seem to be pretty effective as far as I know. I saw Paul Stamets a couple months ago and he seems to think there is untapped potential in many of these polypore mushroom species.