Yes. An E-2 spouse is employment-authorized incident to status and may work for any employer, subject to state nursing licensure. Her job does not affect the principal's obligation to develop and direct the enterprise personally.
Her work is hers; the directing is yours
The spouse of an E-2 treaty investor receives employment authorization as a consequence of her status, without a separate application, and the admission record serves as evidence for employers. There is no restriction tying her to the enterprise. She may therefore pursue nursing, which will require licensure from the state board and, for a first-time U.S.
nurse, a certification for health care workers before she can be admitted in a work-authorized dependent capacity. Her earnings are not counted toward the enterprise's non-marginality, so the car wash must stand on its own numbers. The principal cannot delegate the develop-and-direct requirement to her; if his real intention is to run the store in Saskatchewan while she manages the car wash, the roles should be reversed and she should be the principal, which requires that she be a Canadian citizen and develop and direct the enterprise, ordinarily through at least 50% ownership or operational control.
Children in E-2 dependent status may study, may not work, and age out at 21.