No. You are NOT unreasonable. If Grandma wants to put up with that her whole life, then she can, but you and your family dont' have to. As a mom, I have to say that it's difficult to see one of your kids go awry. Very sad when they spiral out of control and you can't stop them.
My stepdaughter quit school when she was 18, and she's been in jail and has alot of problems, and it's hard to watch that, but I don't expect everyone to just put up with all of her foolishness. When she was 18, we told her, you stop this nonsense, and if you don't go to school, and come home every night and behave yourself, you have to move out. She didn't want to.....so she moved out.
Also, I have a sister who is an alcoholic, drug abusing nightmare, and I finally had to tell my parents that I want nothing to do with her, and if they want to have a relationship with her, that's fine, but I will be visiting them on a day when she's not around. I put my foot down. My sister has mental problems, and she also is a very mean drunk. She has attacked me physically. It's something I just can't forget, and I won't be around that.
You can do that too. Maybe pick Grandma up either Christmas Eve or Christmas Day, visit with her a bit, and then take her home.