As an E-2 dependant she may study but is not employment-authorized; only the E-2 spouse has work authorization incident to status. She could work only through a category of her own, and her dependant status ends at twenty-one.
Children and spouses are treated differently under E-2
The spouse of an E-2 investor is employment-authorized incident to status and may work for the family business or anyone else. Children under twenty-one who are unmarried can accompany the investor and attend school, but they have no work authorization, and working on the crew — paid or unpaid in exchange for board — would be unauthorized employment that could affect her future applications. Her E-2 dependant status also ends on her twenty-first birthday, so a plan built around her staying long term needs a separate route: a student category if she enrols full time, or eventually her own investment or employment classification.
If the intention is for her to take over the business one day, that succession should be planned with counsel well before she turns twenty-one, and the share structure should not be changed in a way that dilutes the parents below the ownership needed for their own status. Document each family member’s nationality with a passport; a derivative spouse or child need not share the principal investor’s treaty nationality.