I don't get how in the post-9/11 world, passengers can still get on a wrong plane (in North America and Western Europe anyway) unless there is a major cock-up on the part of the airline or airport staff. Even if a passenger cannot speak the language of the travel destination, there should be some assistance on hand to help her out. And a look on the boarding pass will usually give away the mistake.

So there must be some numbskull airport or airline staff in OP's case.