An Inconvenient Truth: God does everything for a reason

I am a religious person; I believe in God and all of his creations. However, I have always been told that God has everything happen for a reason. EVERYTHING. For many years, this never bothered me, but 4 and a half years ago, my sister, then just 6 years old, was diagnosed with Type 1 Diabetes. For those of you readers that do not know what Type 1 Diabetes is, it is basically a condition in which your body's immune system attacks your body's beta cells in your pancreas, leading you to be unable to create insulin, a hormone that regulates your body's bloodsugar. You can die within hours of improper blood glucose management and even with proper treatment, you have an increased risk of so many diseases and conditions that would compile a list longer than this blog post. Type 1 Diabetics live on average 17 years less than not Type 1 Diabetics. Uh, gee thanks God, you just took 17 years from my sister's life. Now you may ask if it is hereditary. Type 2 Diabetes, the Diabetes you get from being lazy and fat and eating wrong, is hereditary, but how one gets Type 1 diabetes is unknown, thus my blaming it on God.
I must admit that when this happened to my sister, I stopped believeing in God because I could not fathom how He could do such a thing to my young, innocent sister who I love so much. I always ask myself, "What did my 6 year old sister do to get screwed like this?" To top off our experience with Diabetes, my sister has had two siezures, one of them on the day of her First Holy Communion. She had the siezure in Church. IN CHURCH! Jesus Christ, what the hell! I cried so hard when I saw my sister on the floor, unconscious. The paramedics assured us that she would be fine and that these siezures werer not uncommon; most Diabetics had multiple siezures and he said "We'll see you guys again." I looked at that man like he was an avatar of Satan. But still, he did not scare me as much as God did.
One day, a few years ago, I finally asked my mom, "Do you believe that God does everything for a reason?" She said she did and then I asked her why God gave Caroline, my sister, Diabetes. She told me that she had been thinking about the same question since my sister was diagnosed and she said that perhaps he was preventing her from some other harm. Being an ignorant child, I then asked her what could be worse than Type 1 Diabetes, and she said "Kyle, there are things in this world so terrible, worse than Diabetes." She told me that Diabetes has potential to be life threatening, but after years of my sister having it, we know now that with proper management, it is just a hassle.
I really think that the whole "God does everything for a reason" bothers me because I can't imagine anything worse that seeing my sister lying of a cold floor unconscious because her bloodsugar went too low. So, for now, I can not come to terms with God giving my sister Type 1 Diabetes until I know of something worse that Type 1 Diabetes.