Linus and the blanket have a metonymic relationship. Their relationship is based on contact and nearness, and not on comparison. The blanket is neither a simile nor a metaphor for Linus himself. Further, the blanket itself is a metonym for security, comfort, fear, anxiety, and so on. See?
We know that Linus and blanket are inextricably bound together as a unit. Only because we have come to associate Linus with his blanket over time could we conceivably refer to Linus as “the blanket kid.” That would then be synecdoche, where part of a unit stands in for the whole unit. However, your saying “the blanket kid” outside of the context of the Peanuts comics will not necessarily have the intended effect of suggesting “Linus” to your listeners. Surely, there are other kids with blankets.
Part of the project of Ruth Hall is to alter the metonymic, cultural associations of “woman.” Instead of self-conquest, Fern substitutes self-expression. Notice that the association of woman with motherhood remains.