Hylian7 said:Exactly what I was thinking.
There was this image: http://images1.wikia.nocookie.net/__cb20081219172344/half-life/en/images/6/6d/Vance_family_photo.png
I don't know
since in Portal there were slides that proved that Aperture and Black Mesa were competing with each other which establishes the time frame and GlaDoS implies that the Combine have taken over the planet during the final battle ("Are you trying to escape? Things have changed since the last time you left the building. What's going on out there will make you wish you were back in here. I have an infinite capacity for knowledge, and even I'm not sure what's going on outside. All I know is I'm the only thing standing between us, and them. Well, I was.") and Chell was in cryostasis before the events of Portal (game intro basically). So if we take that into consideration and then the fact that immediately after the battle, Chell is put into Cryostasis for who know how long, it doesn't add up that she could be Alex's mom.