It's not deadly, no, but at this point my mom is extremely sensitive to gluten. Literally one grain of flour would be enough to set off a reaction- the immune system goes nuts when it sees the return of what it thinks is a pathogen. In order to avoid that, I'd have to:
Never let the food touch anything that my mom might touch without knowing it has gluten
Wash my hands very, very thoroughly after feeding or touching anywhere near the food
Never let the tank water get anywhere near anything, as it would have gluten in it
Never let anything from the tank get anywhere near anything
And basically just treat the gluten like poison. It's not, but that stuff spreads like crazy and it doesn't take much at all to make my mom spend a few days being quite unhappy. It's really just a lot of trouble, and since it's possible to provide needed nutrients with things like whole krill and clams, I'm sticking with the gluten-free pellets for now and hoping I can convince them to eat that.