hearing the nice ladies in the assisted living place gush about how wonderful it is to have mom here has really made me cringe inside.
It may be helpful to remember that the "nice lady" the people at the place your mom is living with get to see her "I'm a nice person" face. Which is not the person you get to deal with. My family is full of these folk who are one way to everyone 'in public' and turn into raving loons when they're with family 'in private'. The folks there also do not have the years of history that you have, which will change how you (and they) perceive her.
Good luck to you.