yeasts come in two basic forms, activated (alive) and deactivated (dead).
the brewers yeast she had back then may well have been live- remember, its the stuff they use to make beer, if its not dead, it'll try and brew whatever it gets the chance to brew, and your body is nice and warm and moist and full of things to brew lol- that probably wouldn't do your stomach much good. nutritional and brewers yeast for eating or use as a nutritional supplement is generally sold deactivated (dead) so shouldn't be able to do any foamy brewing stuff in your tummy.
its also possible that you have an allergy or intollerance to yeast. i bloat up and get pretty unwell from any old yeast- brewers, bakers, nutritional, alive, dead, whatever- my body thinks its an invader and repells it, and freaks out while its doing it. if that was the case with you, its likely you'd get the same bloating and sickness from ingesting bread, beer, marmite, etc- that'd be a big clue.
if you've ever eaten any veggie faux meat products, or mainstream cheesy/savoury slightly salty flavoured things (snacks, chips, crackers... eg: doritos), you've probably already been getting a dose of nutritional yeast, most of those products seem to contain nutritional yeast as a flavouring.
you could always just try a little bit, and see how you go.