Possibly. The Child Status Protection Act freezes a child's age during the time the investor petition is pending, so she may remain a derivative even after turning twenty-one, but the calculation depends on filing and visa-availability dates and must be checked for her specific case.
Her age is measured with the petition's pending time removed
Unmarried children under twenty-one qualify as EB-5 derivatives. Under the Child Status Protection Act, the child's age for this purpose is her actual age when a visa becomes available, reduced by the number of days the investor petition was pending, provided she seeks to acquire the visa within one year of availability. A daughter who is twenty at filing and whose parents' petition takes two years to adjudicate may still be treated as under twenty-one if the adjustment works in her favour, but the outcome depends on the Visa Bulletin and the exact dates.
The family should file promptly rather than waiting for a perfect project, keep her unmarried status in mind since marriage ends derivative eligibility, and have the calculation run before assuming she is protected. Her work on the farm does not affect her derivative status, but it may be relevant to her own future eligibility if she is later considered as a separate investor.