I'm not usually devious when it comes to food, I like to tell DS exactly what he is getting, but a little devious trial for you perhaps??
Put down a plate of food and tell her Barbara sent it over? You could even mention a package has been delivered or put the food in an air tight container or covered in tin foil or something, with a note on it, "Dear E, I made you some yummy food. Hope you enjoy it, hugs B"
I mean, I say I'm not devious but I think I'd be trying this if it was my DS eating someone elses food and not mine.