Possibly. The Child Status Protection Act freezes a derivative child's age while the petition is pending, so time spent waiting for the I-526 or I-526E decision is subtracted. What is not protected is delay after approval in seeking the visa, so the family must act promptly once it can.
The birthday is fixed; the countable age is not
Derivative EB-5 status is available to the investor's spouse and unmarried children under 21. Because petitions and visa availability can take longer than a child's remaining time under 21, the Child Status Protection Act provides a formula: the child's age on the date a visa becomes available is reduced by the number of days the petition was pending, and the child must then seek to acquire the visa within one year of availability. For a daughter aged 19 when the petition is filed, a two-year adjudication does not by itself push her out, because those pending days are deducted.
Where the risk lies is in the period after approval if a visa is not immediately available in her category, and in any delay by the family in filing the visa or adjustment application once it is. Marriage before admission ends derivative eligibility regardless of age. Sensible planning puts her birthday, the expected adjudication time and the current visa bulletin on one timeline, and treats her step as its own deadline rather than assuming she rides along with her parents.