Spouses and unmarried children under 21 are derivatives. The Child Status Protection Act can freeze a child's age for part of the process, but the protection depends on the dates the petition is filed and approved and on visa availability, so a 19-year-old's coverage must be calculated, not assumed.
Calculate the child's protected age with the real dates
Under the Child Status Protection Act, the time an immigrant petition spends pending is subtracted from the child's age when a visa becomes available, and the child must then seek to acquire the visa within a year. For EB-5, that means the I-526 or I-526E filing date, its approval date and the Visa Bulletin for the family's country of chargeability all feed into whether a daughter who is 19 today remains a child at the point that matters. Long processing can help by adding pending time, but visa retrogression for the charged country can undo that benefit.
Ask counsel to run the calculation with current processing times and to update it as dates change. If the outcome is uncertain, discuss whether the daughter should have her own plan, such as a student status, so that she is not left out at the end. Marriage before immigration ends derivative eligibility regardless of age.