My Mom, in a care home, goes to a specific room every afternoon and is then aggressive when the HCA tries to get her out. Any suggestions?

Aggressive goes to memory care, a locked facility. Get her to memory care and if she improves, she might get back to the assisted living level.
It sounds to me like the hospital did NOT get her stabilized if the aggression is continuing. Consult the psychiatrist.

Might be a classic case of sundowning:

Sundowning is a descriptive term rather than a diagnosis.
Alzheimer's Compendium (endquote)

At the onset of sundowning. The demons of anxiety, anger, fear, hallucinations and paranoia come out. Sundowning is unpredictable, up and down cycles are present during day and night.

It is difficult for carers to accept a clent's mind is damaged by Alzheimer's Disease. Not only is memory damaged their ability to process thoughts is impaired. This is true for all stages, we never know until the damage is revealed unexpectedly.

Alzheimer's Compendium(QUOTE) Broadly speaking, sundowning is a cyclical increase in agitation (which may include restlessness, confusion, disorientation, wandering, searching, escape behaviors, tapping or banging, vocalization, combativeness, and/or hallucinations) that takes place at roughly the same time every day. Despite its name, and the wide-spread belief that sundowning occurs in the late afternoon and early evening, studies have found that the peak of sundowning activity is more likely to occur in the early- to mid-afternoon (e.g., around 1:00pm), while in some patients, it may occur late at night. It may even peak in the early morning in a fairly high percentage of patients.

Learning person-centered care techniques sounds like a lot of hard work and effort. Actually, the sooner the caregiver begins learning “how to speak Alzheimer’s”, the better off everyone will be, and the less likely that behavioral problems will crop up. Studies have repeatedly shown that caregivers trained in non-drug interventions can not only reduce the frequency and severity of behavioral symptoms and produce higher quality of care.
(endquote)

Wait, the writer didn't say that going to the room upsets her; being forced to leave it upsets her. There's a reason for this, in her mind. She's somewhere important and it's hugely important for her to stay there. No-one has figured out what those two things are -- where she thinks she is, and why she must stay there. For example (I'm making this up, I have no idea if this is it, but I'm giving an example) here it is 3 p.m. In her mind she's a young mother and it's time to pick up the children from school. [It's the oldest habits and memories that endure, remember.] Can you imagine forcing a young mother to leave the block in front of the school without her children!? Of course she'd resist. In the world of dementia/Alzheimer's you have to understand and deal with the patient's reality. Engage her in conversation about what she's doing there. "It's 3 o'clock, eh? It's time...." With some patience and an open mind you'll find out the story. If she's a young mother picking up her children you can then say, "Oh, your neighbor is bringing them home today. They must have left the school already. Let's get home and meet them there!" If she herself is the child and she's waiting for her mother to pick her up, try "Oh, she's over at the bus stop." But then perhaps she won't leave -- because, after all, she was told never to leave the school with a stranger. Then try "It's Saturday! We're already home!" or whatever works with the story in her head. It may take a little doing but in the end it will be a lot less effort than trying to force her to do something that's totally unacceptable in the context of the story in her head.

Why don't they just close the door and lock it if need be? She obviously has positive memories of the former person in that room, and wants to stay there and visit. Drugging her is the wrong way to go. Just occupy her time elsewhere and change the clocks.

It sounds like the best thing to do is change her routine. Have her hair appointment, craft class, walk outside, DR appt at 3, or anything that gets her out of the area. She must have known the person,or something happened that bothered her there. It sounds like Sundowning, or that something she associates with in THIS room at this time, but changing a habit can be healthy and for the better.

Yes, alwayslearning, like a dog waiting for his master (child) to come home from school. Or the Akita who waited at the train station for about 10 yrs. when his master (Richard Gere in the movie) did not return. He died on the spot and the Japanese village erected a statute of him patiently waiting. A real tear-jerking movie...and true.

Dave, thank you for sharing the source Alzheimers Compendium, I didn't know about that and went to alzcompend.info -- is that the source or is it another source?
For all my life past about years old, my Mom was combative and paranoid and in the middle of night be heard maniacally humming and rhythmically rubbing her kitchen counter in a circular motion. It was so frigthening to me, and always, always blame but I could see her snake-frightened eyes. Now you've given a new idea -- that my Mom had some sort of brain damage that emulated this sundowning in Alzheimers. Anyways, the anonymous poem at alzcompend.info shot a dagger in my heart, cathartic. Thank you so much.

Ferris and leolady great suggestions. My initial response was the same. If going into the room upsets her, don't let her go. I also sounds like she might have a mental illness in addition to her dementia since this behavior was prior to alz. OCD or something else. Seroquel can sometimes help with sleep and mental illness both, as well as being sedating/calming. See if you can get another NP or ask the NP why she altered the medications in the first place. Do you have POA? Maybe you can get an arrangement where they talk to you first before changing any medications. I think the "too low a dose" has already been established. Is you mom able to process that her friend has gone somewhere else?