All for a reason?

We are always talking about how everything happens for a reason...but how are we to know if it really is for a reason, or if its an act of nature, God...No one knows for sure. But we all want to have something to say about things that happen that we don't like.
Last night my girlfriend last her grandmother. I was at a loss of what to say...i could tell her i love her, say everything is going to be alright...and i did...but i also said that everything happens for a reason. Did i know the reason? No, i couldn't even fathom why someone would have to die. It hasn't even been a year since she lost her Aunt. How could all this happen for a reason? No one can be sure, so why did i even say it. Because i didn't know what to say. What do you say to someone you love who keeps losing the ones that she loves. Does it make any sense? Is it all for a reason? I can't tell you. All i know is that girl is the most amazing girl i've ever met. She does nothing wrong, so why does she keep losing everyone special to her? I can't answer the question, but i want to be able to. I'm at a loss, and i don't know what to do...I love her more than anything, i'm going to be marrying her and everything...i can tell her anything and everything. But i can't be there for her when she most needs me...and its not only because we don't live in the same town or don't get to talk...i just simply don't know what to say. I lost my grandmother, and it took me two years to finally get over it. That woman showed me life...and it took forever for me to move on. My girlfriend loves her grandmother, but it's her step dads grandmother...should she love her less? Should this death be easier for her than it was for me? I have questions with no answers...I have a love for her than can't be explained...and i'm completely helpless for the one that means the most to me in my life. What can i do...that will always be the question. My girlfriend is strong and will move on...but i don't know how to help her. Maybe later in life i will. But who knows for sure.
Again i ask, do we really know if everything that happens is for a reason, or is it nature, or God?