Transit without a visa

Now that my wife has her immigration papers to come to Canada, and a ticket on American Airlines she has to land in Miami then transfer in Dallas before arriving in Canada. Acording to the Airlines she can fly without an American Visa but the US Customs and American Consulate in Vancouver says she needs one. The INS in Miami says she doesn't need one to transit. Any dominicans out there that have travelled through the states to Canada in the 'TRANSIT WITHOUT VISA' mode or people with spouses that have done so. What happens?

When they arrive in Miami they are escorted by a agent from US Immigration to a special area designated for travellers without US Visas. They must remain in that area under supervision for the duration of the waiting period. (Hopefully not to long). When time comes, they are escorted to their departing flight. From what I heard from some of my employees that I sent to Canada to visit my family "No big deal"