I think that Chell could actually be in Ep.3 or Half Life 3, whichever comes first. Here is my reasoning.
#1: Portal 2 only takes place 27 years after Portal 1.
Since the relaxation vault is on a day timer, waking people up after 50 days, we can assume that the 9999 error that occurs when Wheatley arrives is also in days. This puts the clock at 27 or so years give or take. This seems a lot more realistic that the hundreds of years suggested, since the building is still somewhat intact. Nature can destroy ruins in a matter of decades, and given a hundred years even, an unmaintained facility would be wiped off the earth.
Any information that is given to the player regarding time is either coming from Wheatley or GLaDOS. Wheatley is a moron who makes mistakes, and GLaDOS intentionally lies to you all the time, so you can't trust either of them.
The amount of decay suggests only a few decades of neglect, since the room you wake up in is still somewhat intact. The fact that the Rattman graffiti hasn't worn away yet also suggests a shorter time span.
#2: Portal 1 takes place shortly after the 7-Hour War
Going by the timeline, Chell is woken up some years after GLaDOS initiates the lockdown of Aperture on May 16th 200- (The time in which the Black Mesa Incident occurs)
GLaDOS also claims in the song "Still Alive" "When I look out there it makes me glad I'm not you", suggesting that the surface is dangerous. It definitely would be following the 7-Hour War.
So if we assume that Chell was in stasis for 27 years as proposed by Reason #1, then that leads us to Reason #3
#3: Portal 2 takes place approximately the same time as Half Life 2
Half Life 2 is suggested to take place at least 20 years after the 7-Hour War and the Black Mesa Incident. The timeline sets the date at 202-, giving room for leeway. If Chell has been in stasis for 27 years since Portal 1, that puts her escape in Portal 2 in the ballpark for Half Life 2.
#4: Valve Suggested implementing a deaf or mute character into Episode 3
Looking back at the information we had received regarding Episode 3, it was hinted that Valve was considering adding a deaf character into the story, or at least one who had a disability.
Chell never speaks, and might have brain damage, since you jump to respond to Wheatley. The reason? Emancipation Grills. They are known to corrode Dental Fillings, Tooth Enamel, and Teeth, which would give Chell a speech impediment. According to Portal 2, they can also melt Ear Tubes, which would make her slightly deaf. GLaDOS herself calls Chell a mute at the end of Portal 2.
So, we have a mute, potentially deaf person, alive in roughly the same timeframe as Half Life 2, and Valve had suggested implementing a character with a disability into episode 3.
Insane? What do you think?