Internal development records for the system, standard operating procedures she wrote, validation and audit files, training materials created for company staff, and a personnel record showing how long she has held the role. Alongside those, the corporate documents establishing the relationship between the entities and her qualifying year.
Assemble the artefacts, then let the letter describe them
A support letter carries far more weight when it points to a folder than when it makes assertions. The exporter should collect the version history and design documentation for the traceability system, the written procedures governing depuration cycles at its own plant, the validation records that show those procedures were tested, and any audit or certification file in which the system is described as the company's method. Training decks she produced for staff establish both authorship and the fact that the knowledge is transmitted internally rather than acquired externally.
On the corporate side the file needs share records linking the Canadian and American entities, evidence that both are trading, and payroll confirming one unbroken qualifying year within the previous three. On the placement side it needs the services agreement with each customer plant, drafted so that supervision plainly remains with the affiliate. A file assembled in that order tends to write its own letter.