I believe that traffic laws do not apply on private property. I think she can get the case thrown out. Very zealous Iowa policeman there.
Yeah, they do apply.
Depends on the state, but usually, if you are drunk and in control of a motor vehicle, on the street, or private property, you can be arrested. The charge may not be DUI/DWI, but may be "In control of a motor vehicle while impaired".
