De hecho es la única forma. No te puede pedir tu mama siendo mayor de edad y casada si solo es residente….
La pagina del USCIS dice…
If you are a… You may petition for…
U.S. citizen: Children (unmarried and under 21), Unmarried sons and daughters (21 or over) – Your son or daughter’s child(ren) may be included on this petition, Married sons and daughters (any age) – Your son or daughter’s spouse and/or child(ren) may be included on this petition.
Permanent resident (green card holder): Children (unmarried and under 21) – Your child’s child(ren) may be included on this petition, Unmarried sons and daughters (21 or over) – Your son or daughter’s child(ren) may be included on this petition.