What food is she on?
Have you changed laundry detergents or softeners?
Are you wearing perfumed body lotion or perfume?
Did you spray any air fresheners in your house?
Use a different product to clean with?
In other words, dogs can respond negatively to all kinds of changes that wouldn't mean anything to you. It's possible, like Heather said, that she's become sensitized to something in her food. But it could also be something you're doing, some new or different product etc., depending on how sensitive she is to environmental factors.