Phenobarbital (brand names include Luminal, Solfoton), which your mother takes, is a barbiturate which is used to control epilepsy. Sodium pentobarbital (brand name Nembutal), which is what was in the pet foods, is a different barbituate which is commonly used to euthanize pets and livestock.
The presence of it in pet foods suggests that the foods contain rendered euthanized animals.
Personally, I don't care if the FDA has determined that small amounts of pentobarbital is not likely to cause adverse affects -- would you take barbiturates you didn't need, because they probably wouldn't hurt you? I sure wouldn't.