It sounds like she has developed gustatory rhinitis. This is amazingly more common than you think. A simple google search for “sneezing after eating” pulls up lots of similar complaints. I would venture to guess that this is related to her gastric bypass. By making her stomach extremely small during the bypass procedure, she somehow has become more sensitive to food (that is, when her small stomach stretches, it induces the sneezing, whereas before the procedure she had a much bigger stomach). She should speak to her doctor about this and see if she can try some medications to prevent this from happening. Good luck.