the first thing i'd ask about her depression test - which one is it and how many questions and what is the sensitivity and specificity of the test she uses.

I thought the simple ones that take 10 minutes are just a screening tool - which means that it is supposed to highlight people that might be depressed and you should investigate this further, not that they are absolutely depressed.

In any area of medicine there is no test that is 100% accurate and even more so in subjective fields like psych. If you review the journals, there are entire articles that test and discuss the validity of all these tests.
And psych can be particularly hard to make a diagnosis as so many disorders have symptoms that overlap.
How about asking who cares about the diagnosis? - you want help with the issues that are bothering you right now.