When it comes time that a spouse belongs in a memory care unit, how can that be accomplished against their will?

If you have POA, you might want to do this gradually. I found a wonderful adult day care place right in my town. I didn't ask my husband, but brought him on a short tour and introduced him to the location and the really nice people who worked there. After he was there for a couple of months for 2 days a week, I increased it to 4 days a week. After another month, I took him on a tour of a Memory Care facility. I told him it was like the Adult Care, but nicer and he would have his own room. It was the hardest thing I have ever done, but I was no longer able to keep him safe at home. I'm praying for you and your wife!

Welcome. I am sorry your wife & yourself are faced with this awful problem.

My Mother is deemed able to legally make lifestyle decisions, yet lacks insight & refuses Non-Dad caregivers & respite care regularly.
Doctor said it simple: She does not have the right to enforce a particular person to provide her support. If he can't do it, an alternative is required. Either in home or in a facility.

Welcome!

I think the most common way to overcome a refusal is telling hospital social worker, on a hospital admission, that it is no longer safe for the patient to be at home.

This creates an unsafe discharge, remember that term, and kicks the system into helping you find a facility that can meet her needs.

Best of luck. This step is a challenge for everyone that is/has gone through placement against the patients wants.

If you can’t bare the thought of telling her it’s a permanent move (and who can?) maybe get her there by telling her that she needs to be there for a couple of weeks because of something you must do. Maybe tell her the house needs some work and will be unsafe to live in for her until it’s done, or that you need a minor surgery and when you are recovered she can come home. A friend of mine who needed to place her mom made out a fake prescription from her mother’s doctor and said your doctor wants you to have some tests and it will require you to stay overnight to prepare for the test. That got her there and then overnight turned into “just a couple more days”. She brought to just enough of her mom’s clothes for a few days and then over the next week brought the rest of her stuff. It’s awful, but people rarely go willingly. The best you can do is try to get her there will as little stress to her and you as possible.

There's always the classic reason when moving someone into memory care.

'Your doctor wants you to go into rehab for a little while to get stronger'.

Of course you have to make sure you have POA. You might even want to get appointed conservatorship. This way there's no complications getting her placed.
Do you have a facility picked out already? If not, check a few out and get her on waiting lists. There are waiting lists for these places.
WearyJean in the comments makes a good point. Start sending her to adult day care a few days a week. Even if she fights you on it. She has to get used to you not being with her 24/7. The transition to memory care will be easier.

If you are her PoA then read the document to see what causes the authority to become active. If it is a diagnosis of incapacity, then get her in for an appointment on any "therapeutic fib" or pretense that you think will get her there voluntarily.

If no one is her PoA, then you can consider pursuing guardianship through the court. Talk to an elder law attorney about how this may be done, and the cost.

If she goes to the ER for any reason make sure they know she is an "unsafe discharge" and do not bring her home no matter what promise they make to "help" you care for her in your home -- they won't. They just want her discharged. Talk to the hospital social worker about taking her directly to a Memory Care facility.

The doctor told my SIL to bring up her brother to the ER and tell them that she can no longer take care of him. They told her they weren't her babysitter but it got him into a nursing home faster than anything they could have done.

Or like my BIL he fell at his apartment laid on the ground for 30 minutes until someone found him. He went to the hospital then to the nursing home memory care part. He lived alone.

Prayers you find the way to do it because my BIL would not go on his own.

That is a tough call first make sure you get a poa. My personal experience is most of these places are over packed and have little room and the staff is spread too thin. Mainly as a result of our current times. My aunt lived out her life at a very good one but that was before our current healthcare crisis. Same with my mil. My wife (79) was in a facility earlier this year and it was terrible she actually got worse. I brought her back home with home health once a week and she is getting better physically and her mental state seems to be stable. My tip is do your research and get referrals

So sorry for your situation. Has she been deemed incompetent? If so, are you her POA? If she's not been deemed incompetent, do you think she is and would a doctor say she is to activate a POA?

I think you could try to shift the conversation to "I'm sorry it's not safe for me to take care of you at home anymore." Or that your health is failing and you just can't physically do what needs to be done. You may have to tell some fibs, exaggerate a bit, etc. But you need to take control and tell her what is happening, whether she likes it or not. Don't ask, kindly tell.

If you don't want to be that heavy, you can hire lots of at home care so that it may become tolerable.

If she ends up in the hospital for ANY reason, you will have your golden opportunity to tell the staff that you can NOT take her home under any circumstances and they will help get her placed in an appropriate setting.

Best of luck!

Her doctor could be your best ally by recommending that she be placed for her own good.