Vaping

My 15 year old granddaughter has recently taken up vaping and I have tried to get her mother, my daughter, to talk to her about it as this is not good but she does not seem to care. My daughter has been slightly unstable her entire life and we have a fluctuating relationship dynamic. I have been told by my grandson, her other child aged 10, that she buys vapes for her and I am at a loss. I don’t want to get the police involved as the children may get taken away and I am unfit to take care of them because I have health complications. Their father is nowhere to be seen. How should I handle the situation? Everytime I try and talk to my granddaughter she ignores my advice as I used to smoke cigarettes.