Is it wrong to want my 92-year-old mother to move out 6 months after she moved in with my husband and I?

You are absolutely right to not let this go on any longer. WHENEVER an elder moves in with family there should be an agreement before the move with ALL parties that this may not work. Because often enough it doesn't work. This is a matter of your own life, which you and your husband have a right to. Discuss it gently with your mother and begin to help her with making arrangements for assisted living. This is a matter of GRIEF and NOT guilt. Guilt belongs to felons. Grief is for people who have their own lives and their own human limitations; to think otherwise is to think we are omnipotent, that we are gods. We aren't. We are human beings.
I am sorry; there's no good way out of this but grieving it. You will grieve it and so will your Mom and all others involved. Your intentions were good. It has not worked. Not everything can be fixed. I wish you the best. My heart goes out to you in your grief, and to your Mom, but this has an answer, if a tough one.

You mention your mother is mentally & physically sound, yet posters here insist she has 'cognitive decline' or should at least be tested for it before you do anything at all. I disagree. Your mother was living alone & doing fine prior to you inviting her to live with you, so that's what she should be doing again, now that it's not working out being roommates. You made a mistake. Admit it, sit down with mom, tell her you wanted things to work out, but they're not, it's not that you don't love her, but you love having an empty nest MORE than you love having another roommate, that's all. End of story. Put the blame on yourself; take all the responsibility for the fact that the living arrangement isn't working out, apologize if necessary, and then go about finding her a different place to live.

People make mistakes all the time b/c we're human. What we have a hard time doing is admitting it. Once we do, however, that's when everything changes. Humility allows us to accept our humanity with grace and allows the other person to do so as well.

Once the elephant is out of the room, then you and mom can go about finding a new place for her to live. Whether or not she wants to live with 'old people', she IS an old person herself! Being in a senior apartment complex, she'd have lots of others to socialize with and that would be a GOOD thing, so present it to her in that light. When I had to move my folks here to Colorado, I knew dad was a bit tight with his money, so I found them an older senior apartment building that had great reviews. The rent was a lot lower b/c it was older and didn't have the fancy bells & whistles that the newer chain places had. They wound up with a much larger unit as a result, and loved it there for the 3 years they were residents before AL became necessary.

So stop berating yourself for wanting your home to yourself. I would HATE having anyone living with me and my DH and I say it out loud all the time. It's my right to feel that way, too, and there's nothing wrong with it! I've earned that right at almost 65 years old, too. So have you!

Good luck!

If you are prepared to be blunt, when M says she "doesn't want to live with old people", just tell her that neither do you. There is no ‘nice’ way to get the point across to someone who ‘pushes the limits of every No we give her’.

Not wrong at all.
Have you said to mom what you have said here?
If she is disrespecting the boundaries that you have set then have a sit down talk with her and tell her that after the New Year you will both have to begin looking for Independent, Assisted Living or Senior apartments for her and that by Feb 1st you expect that she will be moving out. (In IL or AL she may be able to do away with the "helper" so that will no longer be an expense)

It's not wrong at all. You had a romanticized notion of what caring for mom in your home would be like. And instead, like so many others on this forum, you discovered a hard reality: her cognitive decline makes her less and less able to see boundaries, and use reason and logic, making her a very challenging housemate.

Hopefully you are your mother's DPoA so that you can help get a cognitive/memory test at her doctor's and then consider transitioning her to a care facility (that accepts Medicaid) where she'll have far more social interaction with different people and opportunities to participate in activities and events. I wish you all the best in working through it -- you are certainly not the first adult child to have this problem and you won't be the last. May you gain peace in your heart in the process.

Unless this new home was built with a totally separate, fully equipped apartment I have some sympathy for your mother, this after all is her home too and she shouldn't be expected to hide out in her room any more than you and your husband should. Have you sat down with her and had a frank discussion about it, or have you just been secretly stewing and irritable and expecting her to intuitively understand that you are the queen of this castle and she is merely a guest there on sufferance? Do you think negotiating with a third party might be helpful?

Six months, huh? You haven't even gotten your sea legs yet. You're right to want her out and it would be best for everyone if you got her out soon. Keeping the situation as is will ruin whatever relationship you have with her.
You say that your mom does not have dementia and does all right health wise which is good. That being said, what you have on your hands is a senior brat. A senior brat is the same as a child brat only old. You deal with them the same way though. You stop allowing your mother to behave like the lord of the manner in your house. This means your word is law and that's the end of it. If like a child brat she throws a tantrum when she doesn't get her own way, totally ignore her. Remember something, you're not a kid anymore. You do not owe mom an explanation for anything you do or anywhere you go. You don't want her living with you and made a mistake letting her move in. Stop beating yourself up with guilt about it. Everyone makes mistakes.
Find her an AL or senior living community and tell her she's moving in. If she gave you any money to build your dream home, give it back. I'm sure she'll give you a hard time about it but too bad.
Could your almost homeless sister be an option? Like the two of them move into a place and mom pays her instead of her 'helper'?
Granted, this possibility will sell your sister into slavery, but it would beat being homeless.

OP, it sounds like even if Mom adhered to every specific boundary you set up, that you'd still be angry--as you said, your imperative is that you want to share the house ALONE with hubs and not her. This does put her in a rough place too as both of you agreed to this.

Have you thought about putting a Tuffshed tiny house in your backyard? It's not just a shed when fully set up, it's a full on in-law separated unit. No dementia or ADL loss? She should be able to maintain "independently" in there and pay her aide/housekeeper/driver. She presses on you for more free labor and stuff beyond that, that's when you bring up Medicaid as you're not Bank of Free Stuff or Director of Socialization.

The unit would also be an appreciating asset. Once your mother passes or is out of there, it can be used as a rental or down the line housing for an aide should you yourself need one.

Maybe she will get it if she catches you doing the nasty on the kitchen table, the couch, where ever you feel like. Embarrass her until she stops with the entitlement.

Have you straight out told her that she is going to have to move if she keeps it up? This is YOUR house, you ARE the mistress and she is not?

Explain that she doesn't need to understand, she needs to respect your desire for some private time with your husband.

You're perfectly right in wanting to keep only your immediate family in your house. Try to get her into her own apartment and then visit her frequently. There is not such a thing as the right of the wrong way of doing things. You and your family should decide what is best for your family group.