This should've ended with this chapter. Instead they milked it with a generic long-running sequel series that turned the shounen-generic-ness up to eleven.
@Raffro
it doesn't directly makes her immortal but something else does, but she is the only person 'lucky' enough to have the other thing happen: for example, there might be only one 'elixir of immortality' in the world but she is the only one 'lucky' enough to somehow end up drinking it.