So my roommate has a mental condition where after a set of stressful events in their life they devoloped this issue where their hand now acts on its own. It seems to argue with them and stop them from completing tasks such as eating, shopping, paying bills, simple hygiene and entertainment.

It seems to have developed a personality. It sometimes is violent to the roommate when it is frustrated. Never violent to other people.

They have seen a doctor and are going to attempt to get a second diagnosis but it was something along the lines of psychogenic seizures with odd/unique hand movements.

My question is does anyone have any ideas on what this could be?

Does anyone know of a therapist or doctor that specializes in this in the California area?

Late to this, but perhaps your roommate might have Alien Hand Syndrome? Also known as Dr. Strangelove Syndrome, Strangelovian Hand, or Anarchic Hand?

I'm not very confident in this answer though because the condition is rare; I only heard about it after one of my professors briefly mentioned it in one of my psychology courses.

Alien Hand Syndrome is usually associated with other neurological problems such as a stroke, brain tumor or aneurysm, or after an individual has major brain surgery or suffers from brain lesions. However, there have been some case studies with individuals developing the condition after experiencing trauma. I'm not sure what "stressful events" your roommate has experienced, but if they involved a head injury or TBI, that could provide support for this.

The symptoms of your roommate you describe match some of the behaviors people with Alien Hand Syndrome have reported, though getting an evaluation/diagnosis for it can be tricky. Along with the rarity of the condition, diagnosing someone with Alien Hand Syndrome is difficult because it's a neurological disorder that displays observable behavioral symptoms that may be associated with some psychiatric disorders instead, which tend to be more common.

Anyways, I could be completely wrong, so take all this with a grain of salt. Also I don't live in California, so I can't really refer anyone specifically, but I'd suggest having your roommate see someone who specializes in neurology, or maybe a neuropsychologist or neuropsychiatrist, depending on the severity of their symptoms and what kind of treatment they're seeking. Hopefully some of this might help! I wish your roommate well!