Presumptions in law can be challenged by the introduction of facts to the contrary. Additionally a jury cannot be compelled to accept such a presumption (juries being the last defence of the common sense in the courtroom.) And speaking of law there is additionally case law. "A violation of this section is one offense, which may be proven in different ways. A person's breath alcohol concentration may be probative of impairment under subsection (1), as well as proof of a violation of this section based solely on breath alcohol concentration pursuant to subsection (3). State v. Kubik, 235 Neb. 612, 456 N.W.2d 487 (1990)" The text of the first section of the local DUI law reads "(a) While under the influence of alcoholic liquor or of any drug;" Gives good reason to believe the true meaning of the statute relates only to the influence of external substances.
Assuming the woman really has the condition she claims to have, driving on a flat may still be considered negligent or careless driving, and the condition itself may be grounds to revoke her drivers licences.