Teenager huffing paint and whipped cream at school

First off I'd like to say that this is about my 14 year old niece. Her father ( my brother) is not in the picture because he is a drug addict so I have been like a second Mom to her and we have been very close her whole life. Here's the story... Twice since December she has been suspended from school for huffing at school, in the classroom both times with the same " friend".She swore these were the only times that she has done this and said she will never do it again. Her Mother and I are at a loss on how to help her. We have told her how dangerous this is. We used every angle that we could think of the first time she did it. We tried punishment, we told her how scared we are for her, we told her how much we love her but nothing seemed to work. She obviously doesn't understand or care that she could die, that it only takes once. I am writing this because we are in desperate need of HELP to save my niece from this horrible downward spiral. What can we do to stop this?