I saw it on Thursday, I thought it was pretty good, with that said I remember watching some anime of it just can't remember if it was the anime or an anime movie (if there was one)
some of the key plot points that really got me as being handled very well had to do with the heart, her friend (boyfriend) and dr syrin.
with that said while its an excellent movie, there are definitely some very sick evil people and plot threads that occur, so I can understand why one of the trailers in the theater I went to, was a horror movie one.
as to her survival it definitely seemed to me that when certain events happened in the past her "core" went into preservation life support mode, which meant that her heart, dialed down to minimal mode which considering the type of power source it is, also meant that it wasn't using fuel very fast. as far as nutrients to keep the brain alive I took that as a combination of setting the life support to a minimum resource use mode, but also question the size of the reserves, and whether the "core" had some way of scavenging from the environment to restock.