This is strictly academic.
How do you determine the relationship between the querent and the person she wants assistance from using the same significator both of them?
Is the Moon the mediator between the querent and quesited?
Good point.
I assigned the 10th to him as a person of authority she is looking towards to receive a favour.
She would be both mercury and moon, her co-significator.
Instinctively I saw mercury in its dual sign of gemini, as potentially representing both. The mercury retrograde, turning direct at about 14 degrees without making aspects summaries the situation: she trying again but without results, and him now retired not able to assist.
If we shift to the 7th, assigning him as the "other" person as Tikana points out, which is of course a valid alternative, the outcome is pretty much the same. Moon promises by its trine to Jupiter, co-ruler of 7th, but the 3rd is not involved, and its ruler is VOC.
The question, after all, was "should I write...." which involves the 3rd.
Neptune on the 7th gives an illusion of hope, but then he is in his own house, and will receive the square from sun confirming it is just baseless hope.
Once mercury turns direct things might change and she could ask again, as the communications situation would have changed.