There's a special formula Chihuahus dry food you can purchase at PetCo or Pet Smart stores. Since Chi's don't have the keen sense of smell that other dogs do, this dogfood is suppose to be formulated for that reason, among other reasons. I would try...

I don't understand why my 1 year old female Chi snarles at me at times. She is so affectionate and appears I'm her favorite parent; but she snarles and shows her teeth at me sometimes when I dress her or take a sweater off of her. I'm not hurting her...