She can be employment-authorized. The spouse of an L-1 principal is authorized to work incident to L-2 status, without needing a separate employer to sponsor her. Permission to work is not permission to practise, however: a regulated health occupation still requires the licence issued by the state where she intends to work.
Work authorization and professional licensing are different authorities
Households routinely conflate the two and are then surprised by a delay that has nothing to do with immigration. Hypothetical example: a transferee moves from a Saint-Cyrille-de-Wendover coating business to the group’s Ohio plant, and his wife, a dental hygienist licensed in Quebec, expects to start in a clinic within weeks; her L-2 status permits employment, but the state dental board sets its own examination and credentialing requirements, and that process runs on its own timetable. Start the licensing enquiry before the move, in writing, with the specific state board.
Two other points belong in the same conversation. Dental hygienist is not among the occupations USMCA Appendix 2 lists, so a separate TN is not an alternative for her. And the children travel as unmarried derivatives under 21, may attend school, and lose derivative eligibility on the twenty-first birthday, which for a family with a teenager is a date to plan around rather than discover.