i LOVED the prologue and the topic too it has so much more potential and I think u did a great job! there are a few things I found a bit cliche, like:

"The most wrong thing of all in the whole entire universe, is my little sister's disease." i found this a bit cliche and i feel that it would be better reworded.

"We were both playing in our totally awesome game room." i did not like this bit because it made it sound too much like a diary entry instead of a first person narration and they are similar but there is a BIG difference.

Lily kept dumping food on her face and in her hair." this line and the next two paragraphs i found very eccentric.

the rest i thought was great.

keep writing! ur good. and if u get the chance, please check out my page.