Final answer:
Lily's mother discourages her from becoming a Birthmother because she believes the role has low prestige and poor long-term prospects, and she sees greater potential for Lily in a more respected career within their society.
Step-by-step explanation:
In the book The Giver, Lily's mother does not want Lily to become a Birthmother because she believes that the role is not as honorable and lacks the long-term career prospects and respect compared to other positions within their society. Being a Birthmother means producing new members for the community, but after a certain number of births, Birthmothers are reassigned to menial labor for the rest of their lives. Lily's mother sees greater potential in Lily and wants her to have a role with more prestige and longevity, which would allow her daughter to have a more impactful and sustained contribution to their community.