A. Foul odors coming from the mouth are a tell-tale sign of advanced dental disease. If you don't brush your pets teeth regularly (once a day or weekly) then there is a good chance that there is pus, bacteria and mobile teeth in the mouth. Pet mouths can be a cesspool for infection and this infection can lead tot he rest of the body causing disease and illness.
I am unsure about the other symptoms you mentioned about her moving her head quickly and it is not very specific or alarming.
I would recommend you go to your vet for a complete oral health examination. Your vet will assess the teeth and let your know if disease is present and the appropriate treatment for what is there (i.e. Dental cleaning +/- extraction of teeth).
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