Probably, if the petition is filed before her twenty-first birthday and the family proceeds without delay. The Child Status Protection Act freezes her age during the time the I-526 or I-526E is pending, but she must remain unmarried and the family must seek residence within one year of a visa becoming available.
File before the birthday and keep moving afterwards
Hypothetical example: a Haldimand County couple plans an EB-5 filing and their daughter turns twenty-one in eight months. Derivative children must be unmarried and under twenty-one, but the Child Status Protection Act subtracts the time the immigrant petition was pending from her age when a visa number becomes available, so a filing before her birthday generally preserves her eligibility through a long adjudication. Two further conditions apply: she must not marry before she immigrates, and the family must apply for the immigrant visa or adjustment within one year of visa availability.
The petition date is therefore the single most important date in the family's plan, more important than the project's closing date or the school year. Do not assume that an incomplete protective filing followed by a supplement will secure CSPA protection; the petition must satisfy the applicable filing requirements, so obtain case-specific advice before relying on a filing date. Set-aside categories under the 2022 Act, such as rural or high-unemployment projects, may affect how quickly a visa number becomes available, which in turn affects her calculated age.