With documents that only an owner would have: source repositories and their ownership, internal design and release documentation, customer licence agreements naming the company as licensor, and the absence of any third-party licence for the module itself.
Ownership leaves a paper trail
Hypothetical example: a Hampton company states in its petition that the warehouse module is proprietary and attaches a marketing brochure. That is an assertion with a picture. The documents that actually establish ownership are the licence agreements under which customers use the module, which name the company as licensor and set out the terms; the internal release notes and design documentation with dates and authors; the repository or version control records showing who has committed to it; and any registration of the software or its trade mark.
Add the consultant's own contribution: the configuration documents she produced for each of the six customer implementations, dated and attributable to her. Redact commercially sensitive detail with a stated explanation rather than deleting silently.