A person traveling on Advance Parole status is still considered a temporary resident until their Permanent Resident status can be formalised. As such, they should continue to use all facilities and procedures prescribed for temporary visitors unless directed otherwise.

Some INS/BCS officers can be incredibly anal and I have even heard stories about people being subjected to Expedited Removal for standing in the wrong line (evidently entering the US citizens line, even in error, can be considered "misrepresentation of citizenship"). Better not to take the chance of having her AP cancelled by an officer on a power trip and simply stick with the longer line until the PR comes through.