Plan for the petition preparation, USCIS adjudication (shortened by premium processing), then admission at the port of entry. She should hand over Canadian day-to-day management before she moves, but the qualifying year must be complete before filing.
Finish the year, file, then delegate
Sequencing an owner's transfer has two fixed points. The first is that the one continuous year of qualifying employment abroad must already exist when the petition is filed; nothing she does in the U.S. afterward adds to it.
The second is that once she is admitted in L-1A, her primary work must be the U.S. executive role. Between those points, prepare the corporate and payroll evidence, draft the job description with the hiring plan, and file Form I-129 with premium processing if the timeline is short.
After approval she applies for admission at a port of entry with the approval notice. Before the move, appoint a general manager for the Canadian company and record the delegation in board minutes, so that she can truthfully describe her U.S. role as her main job.
Initial approval is up to three years for an established office and one year for a new office; extensions run in two-year increments to the seven-year maximum. Hypothetical example: An elevator-maintenance manufacturer wants its owner in the United States before a new sales contract begins. The first review should begin with a dated employment and travel ledger to prove the required continuous year abroad, followed by current corporate records and a staffed role description.
Those payroll and travel records settle the threshold question before a filing fee is spent. The owner should also count prior L-1 stays toward the seven-year ceiling and reserve time for admission after approval. A rushed petition often fails because the proposed delegation in Canada exists only in a future organization chart.