How can my brother and I make Day One at the memory care easier, especially after we leave?

My mother still carries some childhood trauma with her and it's making our job a whole world worse. Her parents had pretty much dumped her at a "home" as a child because they viewed her as a "problem child". This home she always told me about was a sort of Catholic boarding school, and whenever she speaks of it, it's very clear that there were hard feelings of neglect and abandonment. Ever since, my mom has always begged my brother and I never to move her into a "home". Well, she's now 70 years old, with progressing dementia. Most of the time she knows me, but doesn't know who I am. Sometimes she thinks I'm her sister. After 3 years of caring for her full-time, it's time to move her into memory care, where she can get the supervision and care she needs, since I'm only 23 and unable to care for myself at this point, let alone her. We've already gotten a lot of backlash from her. We've long since stopped telling her that we were going to move her, but apparently the idea still lingers. Whenever we're out somewhere, she tells us she'll "be a good girl", begging us to "be fair" to her, and that she just wants to go back home. She's currently in the hospital because she was found wandering and completely lost from her apartment. All she knew was her name when she was in ER. We're going to be moving her to memory care this week. She'll have a private room, and she'll have her dog. I'm trying to figure out how we can make this easier for her. Most people say the same thing - bring stuff they like and will remember, make sure they keep a routine, lie to them about how long they're staying. So on, so on, all good points. But I haven't found anything yet that brushes this issue, where someone might be deathly afraid of being abandoned.  Any ideas?