Take a look at page 93 of the DWP Employment and Support Handbook in the ESA Resources . It states:-
The mental function assessment should be applied in all cases where a specific mental disease or disability affecting mental function has been diagnosed or when there is a condition, whether mental, physical or sensory, resulting in apparent impairment of cognitive or intellectual function.
Your wife could try wording the form so that even a complete idiot would realise that a mental health assessment is required.
Derek
That won't work she would have to find out to put it so a brain dead moron given pictures and words and three weeks to think about it, and the chance to phone a friend might get half of it right