At the beginning of the novel, we see her as a classic Beta, one who is programmed and genetically modified to do her job well, to have a lot of shallow relationships with people, and to be fixated on activity and pleasure. However, it is through Bernard and John that her character is given depth. First of all, she goes out with the antisocial Bernard; this indicates possibly a level of maturity not found in her group of women. Then, when John comes onto the scene, we see her become completely turned upside down over him. She experiences, for the first time, real love and desire to be with someone, deeper than the shallow relationships she's had in the past. We see her struggle with those feelings and that change, and try to fit it into her realm of thinking.
John is the real force for her dynamic status; otherwise, she would have remained a flat, stereotypical character that is highly predictable because of her social class. John in fact does a lot of interesting things to the main characters of the novels; once he comes on the scene, he is a force that changes all of their lives. I hope that helped a bit; good luck!
Wow... that's quite the question. To me, the main way that Lenina gets to be portrayed as a dynamic character is through her interaction with men.
At the start of the book, Lenina does seem to be pretty unimportant except for her somewhat unorthodox attraction to Henry Foster. But then her relationship with Bernard Marx puts her into the spotlight.
Over the course of the book, she stops being an unorthodox character and becomes more symbolic of the orthodox society of the brave new world.
Because of being with Bernard, she meets the Savage. Her attraction to him and his conflict about her is a major driver of the ending parts of the book.
So she becomes important (and is changed) by her interactions with some of the major male characters.