The procedure itself with its revision history showing her authorship, training records showing whom she trained, a sample of investigations she led with redacted customer data, the sign-off matrix listing who may release product, and the US site's implementation plan that assigns her the work. Add a declaration from the operations director explaining why the knowledge is company-specific.
Let the procedure's paper trail speak
Assemble the file in the order that mirrors the analysis. First, the procedure: the current controlled document with its revision table naming the author and approver, and earlier revisions showing how the method developed. Second, depth: a log of investigations over the past three years with the specialist's role in each, the release approvals bearing her signature, and any customer correspondence where her analysis resolved a dispute over a rejected load.
Third, scarcity: the training matrix showing how many staff hold each competence level and the time it takes to reach hers. Fourth, need: the acquired US site's gap assessment, the implementation plan, the training schedule and the milestone at which the site can operate without her. Fifth, structure: the share registers linking the two companies and the payroll record establishing her continuous year.
Redact customer names and commercial terms, but keep enough context that the officer can see the procedure is a working document and not a brochure.