We have had a caregiver in home for a year, but mom is wandering, angry, unhappy, disorientated, and it is time to move her as my 95 year old dads' mind is still intact and although he wants to keep her home, she is just too much for him and the family to manage and we feel she would be happier in a very nice memory care center.
The lunch of course is at the memory care, and after everyone is done eating the aides will offer to show your mom around the place by herself,(do not go along) and will eventually take her to her room while you and the rest of the family leave.
And it's often recommended that the family stay away for at least a week or two, to allow your mom to adjust to her new surroundings and folks helping her.
But of course you can call and check in with the facility by phone daily if you want to.
Please rest in the knowledge that you are now doing not what is best for your mom but also for your dad too.
As for whats the best thing to tell mom. It probably depends where her dementia is. It sounds pretty advanced so I wouldnt tell her. Why get her upset in order to have to tell her over and over again and re upset her.
As far as happy strive more for your mom and dad being more at peace than happy. But even more important is her and your dad's safety
Best of luck to you and your family on this really hard journey