What is Lenina in the Brave New World book?
Lenina works in the embryo room of the hatchery. She is a Beta, very attractive, and in many ways representative of her group, accepting most of the values of her society. However, she has a defect ... she desires a relationship with just ONE man. Remember that in the BNW, "everyone belongs to everyone else." To belong to one person might cause you to feel and threated social stability ("when the individual feels, the community reels"). She has a dangerous relationship with Henry Foster, and is attracted to Bernard Marx because there is something "different" in him.
One of her main functions in the books is to have a relationship with John that shows the difference in their ideologies. She wants a relationship that would be typical for the women of her age; John wants a meaningful relationship (in terms that our age would understand). John's knowledge of love comes from his understanding of Shakespeare, an understanding of love as something important, the knowledge that we belong to the beloved, not to "everyone else."
Each presents a different world view; their justaposition highlights the difference between their world and ours.