Yes. A spouse admitted in E-2 dependent status is employment-authorized incident to that status and is not confined to the family enterprise. She may take unrelated employment, work part-time, or start something of her own. Unmarried children under 21 may study but may not work.
The dependent spouse's options are wider than the business
Households often plan around the assumption that the spouse will run the office of the business being bought, and then find that assumption was never required. Employment authorization for an E-2 spouse arises from the status itself; the annotated admission record issued on arrival is what an employer asks to see, and no separate application is needed before starting. That widens the household's options considerably, which matters when a farm's first two seasons are unpredictable and a second income is the reason the move is affordable at all.
Her own nationality does not affect dependent eligibility, so a spouse holding permanent residence in Canada rather than citizenship is affected only in whether a visa must be obtained before travel. Children may enrol in school and may not work, and a child reaching 21 needs an independent status. Because E-2 leads nowhere permanent by itself, a spouse building a career there should treat her long-term position as a separate question.