From your description, it sounds like your dog has a neurological condition. I would suspect Facial paralysis
with secondary Horner's syndrome probably due to to an infection in the left ear
. So that was a lot of information in one sentence, I will try to explain.
I suspect that your dog has facial paralysis on the left side from inflammation around her facial nerve. The most common cause of this is an infection in the inner ear. Symptoms of facial paralysis include: drooling on one side, inability to blink one eye, and drooping of the lips and eyes on one side of the head. Facial paralysis can also lead to a condition called Horner's syndrome, where one eyelid will droop, the third eyelid (pink bit of tissue) will come out, and the pupils are often of different sizes.
Here is a link to more information about Horner's syndrome: http://www.VeterinaryPartner.com/Content.plx?P=A&S=0&C=0&A=482
What you will need to do is visit with your veterinarian to investigate the underlying cause of these symptoms. Again the most common cause is an inner ear infection, but she will likely also check for abnormalities in the eye, pain in the neck and low thyroid levels. For some animals an underlying cause is never found and the symptoms resolve on their own.
Please let me know if I can be of further help.