With the company's own records. Name the proprietary protocol, produce its revision history showing the beneficiary as author, include validation reports and internal training records, and show that nobody else in the group has been qualified to run it. Length of experience proves nothing on its own.
Show the artefact, not the resume
The weakest petitions describe a long career; the strongest ones point at a document that exists inside the company and could not have been written anywhere else. Here that document is the batch traceability and stability testing protocol. Produce it, or at least its controlled front matter, with the revision history that names her as author and reviser.
Add the validation reports she signed, the deviation investigations she led and the internal training matrix showing which employees have been qualified against which procedures. If the matrix shows a single qualified person, that is the evidence. Then describe the receiving assignment in the same terms: not quality oversight generally, but implementing this protocol at the joint venture plant, qualifying its equipment against it and training named staff.
Where the company is asked why it cannot hire locally, the answer should be specific to the process rather than a complaint about the labour market, because the category is not a labour market test and arguing it that way invites the wrong question.