My girlfriend is not under 18 (that would be illegal!

) so that's not going to work. The high school ID is just an old ID that we found while looking for picture IDs that use her nickname. Also, I think it's too late to write the executive office considering the flight is this Wed.
So I logged onto Continental's site to edit the reservation, and found that it allows me to modify the "traveler information", including the name, DoB, and gender. It looks like this is done to comply with SecureFlight as I see the following statement above these fields:
ID information is required.
The name provided above will appear on your ticket and be used for frequent flyer mileage credit. However, to comply with TSA Secure Flight policy, we also require the traveler's name, birth date and gender match exactly with the ID that will be shown at the airport.
The "name provided above" shows the nickname the ticket was (incorrectly) booked under, and is not an editable field.
So it looks like Continental allows me to update the info that is sent to TSA for SecureFlight verification, but not the one for the reservation. So I guess this is what RichardKenner was saying above about these two checks being totally separate.
However, this does not seem very secure as it is essentially allowing us to use one ID for SecureFlight, while actually going through security with another name (the one on the reservation). Is this going to trigger some flag that would prevent them from printing us the boarding pass?
Why is Continental is so hardline about changing the name on the reservation? Obviously they don't want people transferring tickets to others, but this is more of a 'correction'...surely they would correct minor misspellings on the ticket. I brought this up to them but they just said "It's policy".
So I think what we will do is to get to the airport extra early that day and try to check in and get a boarding pass from the ticket agent. At this point, they'll already have the note saying the reservation was accidentally booked under a nickname, and hopefully the ticket agents can update the PNR with the correct information (that matches the SecureFlight info).