If she is showing response to cervical retraction then the neck is definitely involved.

Within treatment you could do Cx retraction, (passive with therapist control and overpressure), hold 20-30 seconds, repeat x 4.

Try active retraction, get her to bring her hands up to her chin to support the head, then relax the neck (i.e. get her to stop pulling her head back and hold it there with her hands). Hold for 20 seconds. Repeat 4 times.

As she gets better at relaxing the Cx muscles, add overpressure with the hands ensuring not pulling the chin down into flexion. Hold for 20 seconds. Repeat x 4. 4 x per day and add during times off increased stress - i.e. after 15-20 mins of watching iPad - you can download apps with reminders on them that will go off to remind her to stretch.

Cervical retraction is far more effective once the underlying issue, being the C2/3 disc has been dealt with. Again, I would seek out someone trained in the Watson Headache approach nearby to assist further should Cx retraction help, but not resolve the issue.

Let me know how you get on.