Yes, fifty percent satisfies the treaty-ownership requirement, but at that level she must also show she develops and directs the enterprise, usually through the operating agreement giving her operational control. Below fifty percent, the nationality test fails unless other Canadians hold the balance.
Half the shares meets one test; control is the other
E-2 requires that nationals of the treaty country own at least fifty percent of the enterprise and that the applicant investor develop and direct it. Hypothetical example: a Shannon facilities-services owner takes an equal share in a Virginia fire-protection servicing company with its American founder; the fifty percent Canadian ownership satisfies the nationality test exactly, and the Department of State recognizes that an equal partner can qualify if she has operational control or the partners share it in a way that gives her development-and-direction authority. The operating agreement therefore becomes the decisive document.
The remaining conditions apply in full: her capital must be substantial in proportion to the cost of her share and the expansion, irrevocably committed and at risk, and lawfully sourced; the business must be a real operating enterprise producing more than a living for her family; and she must be a Canadian citizen. Her spouse gains employment authorization; children may study until 21. No permanent-residence path follows.