It is possible but precarious. The enterprise must be at least fifty percent owned by nationals of the treaty country, so an equal split leaves no margin, and the applicant must still be able to develop and direct the business despite the partner holding the other half.
Fifty percent is a floor for two separate requirements
The first requirement is about the company: its nationality is taken from the citizenship of those owning at least half of it. If Simone holds exactly half and the American founder holds the rest, the company meets that threshold only while nothing changes, and the issue of a single further share to an employee or an investor would end it. The second requirement is about her: she must be coming to develop and direct the enterprise, which an equal holding supports only if the governance documents leave her with genuine authority.
Where a management committee can deadlock, both partners often assume the status quo protects them, but for immigration purposes a deadlock means neither directs the company. Practical structures that help include a majority holding for Simone with economic terms that compensate the founder, or a clear division of operational authority written into the agreement.