Only while she is unmarried and under twenty-one. Derivative eligibility for a child depends on that age limit, and an EB-5 case can take long enough that a twenty-year-old at the outset is not a child at the end. This should be examined with counsel before filing, not after.
The birthday is a deadline, and it is the household's tightest one
Derivatives in an EB-5 case are the investor's spouse and unmarried children under twenty-one. Where a child is close to that age, the timetable stops being a matter of convenience and becomes the governing constraint on the whole plan. Hélène should take specific advice on how her daughter's age is calculated in her particular route and on what, if anything, the sequence of filings can do about it, since the analysis differs and generalities are unhelpful when a single date decides an outcome.
It is worth planning a parallel route regardless. A young adult who will be studying can pursue a student status on her own facts, and one who will be working needs an employment-based basis of her own; either can be arranged in advance far more comfortably than after a derivative claim has lapsed. The husband's position is simpler: a spouse faces no equivalent age limit.