How do we tell mom to live with us?

Can you get her to move close by instead? That way you can still keep an eye on her.

Moving her anywhere is going to be a major battle. Just do it once into a progressive facilty, assited living to memory care in the same place. You bring her home, you'll regret it very soon and then have to have the moving battle again.

cmagnum- unfortunately we can't count on her Dr. to back us up. We asked him to do that after she was in a car accident and we took her keys, and he referred her to DMV because he didn't want to be "the bad guy".
My husband has POA ad has his name on her bank acct.
My plan was to have her here just for a short time. When she started to wander, get mean, or I just felt it was too much stress on us, we would find a memory care facility.
Some days she seems so coherent, its hard to know what to do. = (

I hate to say this so bluntly, but I've often read stories here where the elderly MIL creates hell for their adult child's spouse and marriage. Don't go there. Find another way for her to be cared for.

Has her doctor told her that it is not safe for her to be alone? If not, I would go that route by informing him ahead of time as to what is going on and let him or her carry the blame. I sure hope that your husband or some family member has durable and medical POA for her. Without those documents, you will have to wait until she is not longer mentally competent to file for guardianship.

You can't force her, because if you do she will be very resentful. Can you convince her to accept help in her own home?

I see from your profile that your mother has Alzheimer's/Dementia. I can understand why you would want your Mom to live with you, but first read this Aging Care article about parents who did move in so you can see what the future would be like and if you feel you are ready.

https://www.agingcare.com/articles/Living-with-Elderly-Parents-Do-You-Regret-the-Decision-133798.htm