Sorry I messed up on the time frame - that does make a big difference. It would qualify this as sudden onset aggression and many times there's an organic cause, often with the thyroid, but it could be a tumor or disease elsewhere as well (usually brain-related for neuro symptoms like this).
Some studies through Tufts University suggest that this behavior is related to a 'partial seizure disorder', although it frequently shows as aggression upon awakening.
Taking your companion to be evaluated for underlying causes would be prudent and explaining the course of symptoms to the vet, plus suggesting the possiblities mentioned. Some vets may be experienced with this as a symptom, while others may not believe there's a connection.
It may involve a battery of tests, but the vet should offer them one at a time, step by step, eliminating things as they move along.
With your experience and obvious devotion to this girl, if it's ultimately behavior related, I'm positive it can be addressed with some modifications and positive reinforcement of positive behaviors; however, now that the time line is clear to me, I'm strongly leaning in the direction of an organic cause and she needs to have it diagnosed (and in most cases, there's treatment).
I hope it's something very simple and would appreciate it if you checked back to let me know. God bless,
Many have forgotten this truth, but you must not forget it.
You remain responsible, forever, for what you have tamed.