Either A) the gf's mother stole her identity and impersonated her on the loan application, B) she's lying to you and is going along with it, or C) the inquiry is unrelated to the mother's loan.

Your lying and misrepresenting the facts and reality to suit a narrative. 

Probably not.But the basic dynamics don't lie.

How do you tell when a tenant is lying ?

I think if most were honest and took self accountability we would see where the problem trully lies 

Did they lie about any of those questions?

Floor is just painted concrete, and that includes the 300sf which the county assessor counts as fully finished.I'm reading that DSCR rent appraisers may not count partially finished space at all, and count fully finished basement space at only 25% of the rent of main floor space in the same house.What are your thoughts--is this how it typically is for DSCR rent appraisals?

I think some of the answer lies in your personal goals and in the amount of money you have available to you.

As much as I get tired of reading @Joe Villeneuve saying % is a lie and will mislead you, he is correct in this regard. 

It looks like the ADU has not been properly zoned to be considered it's own unit, so according to the tax assessors report the property is a 3-bed SFH.