You say your wife has challenged, presumably through the link above, therefore the discount is secure - yes, through link you posted.
Wifey parked in a local council car park for work - yes.
So, a regular user or one-off? 5 - 6 times per year.
Familiarity with the machines and procedures or not? Not really, 5 - 6 times per year.
The m/c has a window in which the user can check their input prior to paying, or not? Yes.