Authorship and contribution records inside the product itself: architecture documents, repository history, release notes, internal training materials and a technical statement explaining what she knows that the industry does not. The record should exist before the petition, not be written for it.
Let the product's own history testify
The strongest specialized-knowledge evidence is contemporaneous. A scheduling platform for offshore-supply logistics has an architecture, a data model and a history of releases, and each of those artefacts can show who built what. The employer should assemble the design documents for the ingestion and scheduling components with her name and dates, the version-control history summarizing her commits and reviews, release notes crediting the features she led, tickets showing her as the resolver of the platform's hardest integration problems, and the slides or recordings from internal training she delivered.
On top of that record, a statement from the chief technology officer should explain in plain language what makes the platform's data model unusual, why an engineer hired in the U.S. market would need many months inside the company to reach her level, and why the operator's integration depends on that level. Avoid superlatives and avoid claiming she is the only person alive with the knowledge; the test is distinctness from common industry knowledge, and a credible, dated record proves it better than adjectives.