Let’s first note that God doesn’t “plan” for anyone to be single. If a woman is single, it can be for any number of reasons, but it is not because of some predetermined destiny given her by God.
This is important because we have to acknowledge that the vocation to marriage is the ordinary means by which families are created. If a woman never married, for whatever reason, then there is no reason she should assume that God “plans” for her to become a mother outside of marriage. Even the Blessed Virgin herself, who had very likely committed herself to lifelong virginity at the time of the Annunciation, was called to marriage to St. Joseph before she was called to be the Mother of God at the message of an angel.
What does this mean? It means that a single woman should recognize that children deserve a mother and a father. That children’s best interests are served by a traditional family unit. That it is the children’s needs that are more important than her own desires, and that she should not treat adopting a child as a workaround to the traditional family she was unable to create with a husband.
Bottom line: While there can be circumstances in which there is no other appropriate option for a child except for placement with a non-traditional family (which includes single-parent adoptions), preference should be given to traditional family adoptions, and a single woman should not seek out adoption as a means of fulfilling her own hopes and dreams.
