Hi Nik,
AS and ADHD can be very hard to distinguish, especially in girls/women. And sometimes they co-occur. I hope your tester has a lot of experience with both spectrum and attention issues.
In your shoes I'd phone them about the GADS and ask them the question you posted here about how you should fill it out... see what they tell you to do. Especially since there is a lot riding on it (whether they decide to test further or not) you surely want to do it accurately.
Our practitioners use the ADOS as the best test for distinguishing who's on the spectrum, not GADS. The ADOS is more thorough and has different modules that are tailored to different age groups; it may be more appropriate for your DD. It doesn't take long to give (45 min.) and is very informative.
If she's spending time reading about diagnoses, she may just be trying to figure out why she's different. This is tough stuff at any age, harder for a teenager. Having an accurate diagnosis (if one is appropriate) might help her start to make sense of her difficulties. I'd find it unlikely that she's purposefully mimicking a disorder, though I suppose anything's possible.
If she is highly anxious or impulsive, some behaviors may look "chosen" that are really driven by anxiety or impulsivity. Our DS is like that; sometimes his choices are wholly unreasonable from others' perspective. It is very frustrating for the people around him; it looks like sheer manipulation, but he's sometimes terrified and behaving accordingly. Anxiety meds and attention meds both made a difference for him, as did behavior therapy.
HTH
DeeDee
