Miss Manners: Relative comes for dinner but barely eats my food

Dear Miss Manners: We have a relative whom we always invite when we host dinner parties, whether it’s for a holiday or just for fun. She always replies that she’d be happy to attend.

My issue is that she doesn't eat our meals. She will place small amounts of food on her plate and maybe eat half of it. Her excuse is always that she's just not hungry at the moment. She behaves this way at the homes of other relatives, too. However, if we go to restaurants, she eats everything she orders.