Grandma won’t visit her grandkids.?

This is something I can not figure out. I have twins they are 5. My husband’s mother was there for the birth, but has only come to our home maybe 10 times to see her grandkids.(she and I have always got along.) While my husbands sister has 4 kids, Grandma is always at their house, I don’t understand this, she does not even call to check on them, when I call her I basically have to ask her to talk to them. My husband says the reason she doesn’t come to our home is because I don’t allow anyone to smoke around my kids. I myself am a smoker but I go outside to smoke. This is really starting to make me mad, especially when the twins ask where Grandma is. It’s not like she lives far away only 6 miles. It’s hard for us to go to her house because her new husband works nights and sleeps all day. Any advice on how to address this situation. Or should I just ignore it and when my children get older let them address her on it? I’m confused I want what is best for my kids.