Is an expiatory offering (kaffarah) for an oath (yameen) incumbent upon the questioner because she swore to her friend to eat, but she refused?

If this sister does not fulfill the oath, and instead breaks it and eats of the food, then she owes expiation for breaking an oath. If a food preparer swears an oath upon someone to enter, and the other person swears an oath not to enter, the first one breaks his oath because he swore an oath concerning something he does not own, and there is no breaking of an oath for the second one because he swore an oath concerning something he does own. However, if the one upon whom the oath was sworn obeys and enters, then there is no breaking of an oath for the food preparer.