She has to be properly prepared to understand the sacrament she is to receive. If she has not yet made her first confession, she must also be prepared for and receive that prior to receiving First Communion. Although many parishes route adult Catholics seeking to complete the initiatory sacraments – baptism, First Communion, confirmation – through the RCIA program, the RCIA program is intended primarily for adult converts to the faith, not for adult Catholics. If your daughter’s parish requires that adult Catholics in your daughter’s situation go through RCIA, your daughter, since she has the special circumstance of military duty, can ask her pastor for alternate preparation. She can also check with the Catholic chaplain of her base for programs that may be offered to Catholic military personnel through the Archdiocese for the Military Services, USA.