I am not an instructor in Aikido, but I belong to an organization that teaches and tests for proficiency in various weapons for use on stage.
The spot promotion idea seems to work for now -- but what about the future when/if she is ready for higher rank? Would you spot promote her to shodan? Or after a few passes based on experience and "in-class observation" do you have to say "now you have to test". THEN it seems to me that it would become a bigger, hairier deal for her.
I understand the desire to not have to function as therapist, but it seems to me that you are merely postponing the inevitable. Also, I believe that testing provides its own lessons.
As a sidenote, are there any feelings of inequity from any of the other students that, in their eyes, she doesn't have to test?