Sending you a hug.
Her father is wrong to blame you in any way, shape, or form, but he is a grieving parent and therefore he's truly not in his right mind now. Whatever he thinks he could have done differently "to fix it" would not have made any difference...it's clear he knows very little about addiction or addicts.
Take a deep breath and don't let his grief-borne anger and ignorance make this your load to carry. Remember your troubled friend is now free from her pain and there is some small grace in that.
You did what you needed to do. It's okay.