She can accompany him as an E-2 dependant and, once admitted with the spousal notation, is employment-authorized incident to status. Her nationality does not matter for dependant status, though she will need an E-2 dependant visa rather than a port-of-entry admission if she is not a treaty national.
Dependant status follows the principal; work permission follows the status
The treaty-nationality requirement applies to the investor and to the ownership of the enterprise, not to the spouse and children who accompany him. A spouse who is a permanent resident of Canada but a citizen of another country may qualify as an E-2 dependant regardless of nationality. Both spouses need the appropriate E-2 visas before seeking admission: treaty investors are an exception to the general Canadian-citizen visa exemption, and the spouse applies for an E-2 dependant visa.
After admission, an E-2 spouse is employment-authorized incident to status and may take any lawful work, including a role in the contracting business or unrelated employment, subject to any state licensing the job requires. Unmarried children under 21 hold dependant status, may attend school and may not work. A permanent-resident spouse should also keep her Canadian residency obligation in view, since extended absence from Canada can affect her PR status independently of anything in U.S.
law. Each of these is a separate track on the family's calendar.