One narcissus among the ordinary beautifulflowers, one unlike all the others! […] (1-2)
The first two lines emphasize one-ness, singleness. Because the first line is enjambed, the reader is able to believe this refers to Persephone and the flower. Nifty, huh?
[…] No one heard her.No one! She had strayed from the herd. (7-8)
The speaker repeats the phrase "no one" to contrast with the first two lines. The exclamation point also contrasts with the uniqueness Persephone desired. She's unique all right—she's completely and totally by herself. Now she is isolated, like a vulnerable animal, cut off from the group.
[…] Stickwith your playmates. Keep your eyes down. (11-12)
The speaker emphasizes her motherly advice to Persephone and to us, the readers. The imperative verbs command us to go along with everyone else. The mother clearly would rather see her daughter conform than come to harm, but does it always have to be one or the other?