I don't have any experience with GIEPs, but from what they said about signing something, I would ask if you can see whatever it is they want you to sign in advance of the meeting. That way, at least you will be prepared to tell them why you don't want to sign it, or even if you stay hush during the meeting, at least you will know what they're thinking before the meeting. (Although I defer to others who have actual experience with these meetings.)