What about asking someone to offer her food, and you sharply say NO? Then give her some food and some praise when she does as you ask. Or you could try putting something bitter on the food your friend offers her. I think they have bitter sprays on the training sites that discourage dogs chewing on things. Try these things over and over again, and she should get the idea. You could ask a few friends to help out so she gets the idea only to take food from you, and doesn’t think the food is only bad from one person.