Bell's Palsy can be caused by trauma and it can also have a delayed presentation after the trauma, although usually not after a 2 month time frame and IF you didn't additionally sustain head and or a facial injury during the dog attack, a condition like Bell's Palsy is very unlikely to have been caused by the type of trauma injury you are saying happened during the dog attack...
"What causes Bell's Palsy?
Bell's palsy occurs when the nerve that controls the facial muscles is swollen, inflamed, or compressed, resulting in facial weakness or paralysis. Exactly what causes this damage, however, is unknown.
Most scientists believe that a viral infection such as viral meningitis or the common cold sore virus—herpes simplex—causes the disorder. They believe that the facial nerve swells and becomes inflamed in reaction to the infection, causing pressure within the Fallopian canal and leading to ischemia (the restriction of blood and oxygen to the nerve cells). In some mild cases (where recovery is rapid), there is damage only to the myelin sheath of the nerve. The myelin sheath is the fatty covering-which acts as an insulator-on nerve fibers in the brain.
The disorder has also been associated with influenza or a flu-like illness, headaches, chronic middle ear infection, high blood pressure, diabetes, sarcoidosis, tumors, Lyme disease, and trauma such as skull fracture or facial injury."
Hope that helps......JJ