Everest is somewhat of a hobby for me... a personal goal to trek to base camp (not necessarily climb; though I suppose I would attempt it if the offer was made to me).
Cerebral edema is actually somewhat rare (the rarity diminishes though as one moves above 4,000 meters) and quite preventable by acclimatizing correctly; I've yet to read any information regarding her and her husband's acclimatization for the climb, though they were experienced mountaineers so I feel sure they attempted to acclimatize as well as possible. Two of the other deaths were in the same climbing group as Strydom and her husband (who is expected to be OK physically); perhaps the acclimatization techniques for this particular outfitter didn't work to the fullest for these particular climbers. Everybody is different, requiring different levels and speeds of acclimatization; I think the trick is being able to identify what is working and what isn't. Regardless of acclimatization though, some people's systems simply cannot handle the atmosphere (or lack of it) at that extreme altitude.
There's also been a Sherpa die this year (fell whilst fixing rope 150 meters below the summit) and last I read, there is still an ongoing search for two lost climbers.
Strydom was quoted by her family as saying that she didn't take risks (other than calculated risks I guess); I'll assume that the symptoms came on very suddenly or that she tried to fight the symptoms off between camp three and four. Believe it or not, Everest is a calculated risk; something like 300+ have safely reached the summit this season (though frostbite has been a big problem this season).
Vegan is vegan I guess; nothing wrong with a whole foods plant based diet (could throw some meat in there a few times a week; that's how my wife and I do it). I applaud her and her husband for attempting the seven summits and attempting Everest; I just wonder if her husband feels that the calculated risk was worth it. Once you're there, nose-to-nose with that beautiful pile of snow/ice covered rock, and in the midst of the climb, all that vegan-this vegan-that likely goes out the window and you simply want to survive as your body begins to cannibalize itself.