It sounds like your friend has something else going on entirely because most vegans either don't take supplements or if they do they take B12 and/or D. Interestingly enough, a large percentage of non vegans are deficient in vitamin D, particularly in the US, it's not really a diet thing. It's more of a sedentary office lifestyle causing us to miss out on the sun thing. And you don't have to take B12 if you get it from fortified foods, many of which are already things non vegans consume regularly and where they get their B12 from as well. Your friend just may have other things going on that they don't feel comfortable discussing with you, or maybe they're misinformed about what they actually need to take (which isn't a far stretch since the general population is as well thanks to advertising and marketing).