Alzheimer's in Her 50s?

My younger sister, Carolyn, at the age of 64 was diagnosed with Alzheimer's in October 2012.  The disease has progressed so fast, she is now in an Alzheimer's unit "locked in prison" as she calls it.  She is single with only me, a cousin and an aunt to take care of her.  Thank God there are 3 of us to figure out all this stuff.  It is overwhelming!  Alzheimer's at 51?