I just don't trust my AS alone with my granddaughter, who is the most prescious thing to all of us.
Yeah, I wouldn't either.
Just because they want to live in denial and pretend world doesn't mean you should participate.
Stay squarely in reality. Say what you mean, but don't say it mean: "Mom, you may not leave dear grandaughter alone with AS. I would not leave dear grandughter alone with ANYONE who drinks the way AS does, so I will not be allowing her to stay with AS alone. So just let me know which visit days are good when I can know that only you will be in charge of dear GD." End of story.
If she defends or says -- oh it's only 5 minutes here and there, try the "Hunh." or "Oh" response, which always works to disengage and prevent ratcheting up of drama. Then repeat your rule. "Well, it's just the way it is, she cannot be left alone with AS, so...."
Gets easier with practice - but other than making sure your GD is safe and sound when visiting mom, leave those two to their own fantasy. Never feel bad about living in reality- and if something needs to change you have to choose something that YOU can change - because that's the only power you have!
peace,
b