Under the terms read on the official page, joining family means a spouse and unmarried children under twenty-one, each with their own fee and gift. A twenty-three-year-old is outside that description and would need her own basis.
The family terms follow ordinary derivative rules
The official FAQ, as checked on September 7, 2026, described including a spouse and each unmarried child under twenty-one, with a further US$15,000 processing fee and US$1 million gift for each. Those are the same relationships that ordinary employment-based immigration treats as derivatives, and an adult child does not fit them regardless of the family’s willingness to pay. Her options include her own Gold Card application if she separately pays the required amounts and is otherwise eligible for lawful permanent residence, admissible and has a visa available, or a later family-sponsored petition once a parent is a permanent resident, which is subject to the adult-child preference rules and visa availability.
Do not build the household plan on an assumption that she can be added after the fact. For the younger children, note their birthdays: inclusion at the time of application does not by itself freeze age, and the way the subsequent EB-1 or EB-2 process treats a child who turns twenty-one should be confirmed with counsel before payment.