Totally wrong for two reasons: 1a) the Aincrad arc and to much lesser degree also the Alfheim arc are told in non-linear way and thanks to that to the reader the first girl is actually Asuna 1b) anime made the story linear but also had the fight with floor 1 boss so Asuna is still the first girl 2) the full backstory of Sachi is in volume 2 which is a collection of short stories some of which were hacked into the original story with a dirty axe and in fact none of them are integral to the original story