Jag har en teori!
Well, as it turns out in Portal 2, Chell was brought into Aperture Science at the "Bring your daughter to work day", which, unfortunately, fell together with the "Switch on GLaDOS" and the "GLaDOS kills everyone inside Aperture Science"-Day. If we assume correctly, Chell was in stasis of some kind which still allowed her to grow (or in a growing chamber of some sort) and was awoken by GLaDOS to begin testing. She could have been "stored" in another complex or part of the complex (which is vast as seen in Portal 2), and so the greeting seems to be correct.