How do you deal with not knowing how long the misery of caring for your mom in your home will last?

Are you POA?
If so you can place her in Memory Care or other facility that will be able to provide the care that she needs.
If there is no POA you may have to obtain Guardianship
the other option would be to say, (next time she is in the hospital) that you can no longer safely care for her and work with a Social Worker to have a Court Appointed Guardian (that is if you do not want to be her Guardian and there is no one else)

I’d deal with it by making sure that her time in my home would NOT last. You’ve done too much already.

It’s your home and you’re entitled to your peace and enjoyment of it. She can go somewhere else. Don’t just sit there and let her mental illness and old age keep you in a chokehold. Make plans starting today to move her out.

How long the misery lasts is up to you. From what you are describing it sounds like she needs 24 hour supervision? If so, she can qualify for nursing home Medicaid. That is where she needs to be, in a nursing home. Have you had her get a needs assessment done? If not, get help from the social worker at the local hospital. Tell the SW you are unable to be the caregiver anymore. If you don't like the idea of placing your mom in a NH, then you are going to have to continue on as you are and cope the best you can. Maybe that means being tougher with your mom, setting limits, and calling her out on her bad behavior. You deserve to have friends over if you wish and to have a life.

ER dump her next time she's in the hospital. Her care is not your responsibility.

Does she qualify for Medicaid, if so, that is the answer. There are alternatives you need to explore them.

You are entitled to a life, time to think out of the box, no need to give up your life for her, she has lived hers on her own terms, you might want to give that premise a whirl.

Why can she not be cared for for in a Nursing Home?

What has her geriatric psychiatrist prescribed for her, especially for the sundowning?

Did you discuss placement with Discharge Planning during this last hospitalization?

Are you her POA? Have you visited an Elder Law Attorney to discuss options?