Lezlie, HUGS. I am so sorry for the tragic loss of your daughter. The shock and devastation must've been, and still must be, immense. Please do *not* blame yourself. The addiction to inhalants is SO powerful, especially since they are so readily available, & a lot of businesses seem to not be aware of the issue.
There are other people on these boards who, unfortunately, are in your shoes with how they've noticed that stores and businesses may not have the awareness of inhalant addiction and how products that they sell in stores can be used for huffing. My friend actually has a severe Brain Injury from inhalant use at the age of 12, now in her 30s.
With regard to the grieving process, I'm not sure if you're familiar with the non-profit organization "The Compassionate Friends," but they might have a local support group which is primarily for parents who are grieving the loss of a child. (Siblings, grandparents, aunts, uncles and cousins may attend, too.) Here is the website: http://www.compassionatefriends.org