Had it not been a projectile, it would've have been pills, or a rope or something else. When whatever ill-fated reasoning force finally overpowers the will to live, the tool for which the deed is accomplished is no longer significant, only convenient. Please do not bear in any guilt for this tragedy, but instead revel in the blessed memories the two of you created and shared for the 21 short years our Lord gave to the two of you.
My heartfelt prayers are with you, your family and your daughter's soul tonight.