The woman (child) this song is named for, is dying. Nothing makes people feel sadder faster then a child dying (this time of leukemia) and people like Martina McBride have made whole careers out of it (download God’s Will for a rather awful example.
So having this song starting with diagnosis and ending with her dancing at the prom–one is reminded about Wilde on Dickens (One must have a heart of stone to read the death of little Nell without laughing.) But they pull it off, its not mawkish at all.
The song features plain detail, common speech, little detail, and a touch of clinicism (actually mentioning blood flow and surrival rates) The plainness, the lack of hand wringing, the complete and pure rigor moves away (in fact refutes) domestic melodrama.
I am shocked Rascal Flatts had it in them.