With the records that show the exact dates: records of employment, payroll registers and the rehire letter. The petition then identifies the unbroken twelve-month period that falls within the three years before filing.
Let the payroll register decide, not the memory of the manager
The continuous-year requirement is applied to actual employment, and a layoff, even one where everyone expected the person back, is a break. Assemble the payroll register for the full period, the record of employment issued at the layoff, and the letter that rehired her into the year-round role. Mark the start of the unbroken period and count forward twelve months; if that date has not yet arrived, the petition is premature and should be scheduled rather than argued.
Separately, list any days she spent in the United States on business, since time worked in the U.S. for the same employer does not count toward the year abroad. Keep her duty descriptions for both the seasonal and the year-round roles, because the qualifying year must have been in a managerial, executive or specialized-knowledge capacity, and a first winter spent as a site supervisor may or may not qualify.
Preserve the original French documents and provide translations of the ones the petition relies on.