Caroline, I think that looking for dietary supplements which may reduce the risk of AD is a good plan.

My wife has begun to do this - her maternal uncle died from AD as well so she is concerned about genetic risk factors.

The information in this (fairly technical) paper could help you and your friend to decide which dietary supplements might be of benefit; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4202787/ .