Yes. A spouse admitted in E-2 dependent status is employment-authorized incident to that status, evidenced by the annotation on Form I-94, and may work for any employer or independently. Children under 21 may study but may not work.
The dependent spouse is not confined to the family business
E-2 dependent status gives a spouse wide latitude. No separate employment authorization document is needed, and the annotated Form I-94 issued on admission is what employers ask for. She could work in the yard's office, take unrelated employment or start something of her own.
Her nationality does not affect dependent status, so Canadian permanent residence rather than citizenship changes only whether she needs a visa stamp before travel. Unmarried children under 21 may attend school and may not work; a child reaching 21 must obtain an independent status, and a household with a teenager should plan that in advance. E-2 is granted for renewable periods while the enterprise continues to qualify, so a family can remain for years, but it confers no permanent residence and does not lead there on its own.