Possibly. The Child Status Protection Act may freeze her age during petition processing, but the calculation depends on filing dates, approval dates and visa availability. Get the specific dates reviewed before filing.
Her age is calculated, not assumed
An unmarried child under 21 may accompany or follow an EB-5 investor as a derivative. A child who is 20 at filing will pass 21 before a multi-year adjudication ends, so the question is whether the age-protection rules preserve her eligibility. The statute subtracts the time the investor petition was pending from the child's age on the date a visa becomes available, and requires her to seek the visa within a year of availability.
That formula can rescue a child who ages out during a long adjudication but not one who ages out during a visa backlog after approval. The outcome depends on real dates, so the family should record her birth date, the intended filing date and the visa bulletin position for the investor's category. If the protection will not reach her, she may need her own route, such as a student visa followed by a category of her own.
Marriage before admission ends derivative eligibility regardless of age.