Guys I do not think it will work. She is from Bulgaria which is in the EU but not on the EU eligible countries to enter Canada. The thing then is can she enter with the said EU passport and the US Naturalization Certificate proving that she is also an american?
the site says:
Visa-exempt foreign nationals are expected to have an Electronic Travel Authorization (eTA) to fly to or transit through Canada, starting March 15, 2016. Exceptions include U.S. citizens, and travellers with a valid Canadian visa. Canadian citizens, including dual citizens, and Canadian permanent residents are not eligible to apply for an eTA.

Yes but would AA accept a citizen naturalization certificate and an EU passport that does NOT grand entry by itself? Thats the big question