score:5
As per Timatic, the database used by airlines:
Nationals of Mexico are allowed to enter with an expired passport.
In addition:
Passport Exemptions: Nationals of Mexico with a:
national ID card
certified copy of birth certificate
consular registration
certificate of Mexican nationality
Matricula Consular
- Constancia de Identificacion
Because these are requirements for entry to Mexico, I just called immigration at Mexico city airport, who said that, if you enter Mexico on a Mexican passport, you also have to exit on a Mexican document, and expired Mexican passports aren't accepted for exit, but the listed alternative documents, if valid, are.
So if your daughter has a valid Mexican national ID card (cΓ©dula de identitad personal) or birth certificate, for example, she can leave Mexico.
All of this said, Mexico does not do exit border checks at airports, so if anyone it is the check-in/gate staff that will be enforcing the rules. If they don't want to check you in/let you board as a Canadian without an FMM, present a Mexican document