On the surface Joan Gilling appears to have followed a path eerily similar to Esther’s. Both girls were high academic achievers, both dated Buddy, and both end up in a psych ward. The fundamental distinction is in their demeanor: whereas Joan has a tendency to yield to outside influences while perpetuating a self-confident guise, Esther delegates her trust and admiration to people sparingly and has been experiencing spells of self-doubt. So what role does Joan play in Esther’s narrative? Notice how Joan explains she was only inspired to kill herself after religiously following Esther’s story in the media -- this does not discredit her mental instability, but rather serves to corroborate it. And why did she kill herself? Does she want to be Esther or with her? True, Joan does appear to imply she has feelings for Esther and may even feel wounded that Esther would sleep with Irwin, but all things considered, this detail is far too inconsequential to be the reason for her suicide. It seems much more probable that with her release from the asylum, Joan has tricked herself into thinking that her mind has been cured -- to the point where even Esther is envious -- making her return to the institution that much more traumatic, almost as if her recovery has somehow been invalidated.
If Esther and Joan are so similar, how did only one manage to kill herself? Does it betray how susceptible Esther is to the same fate? Or is Joan a metaphor for Esther’s illness itself? And though The Bell Jar draws heavily from Sylvia Plath’s own experiences, is there a possibility that Joan partly exists as a parallel manifestation of Esther’s symptoms? Consider this: Esther is at rock bottom when she first encounters Joan in this period of her life -- physically grotesque, weak, and a shell of her former self -- while Joan emits a peculiar exuberance and an air of self-assurance. Their initial interactions are rather hostile, with Joan constantly flaunting her superior social skills and recreational privileges in front of Esther while Esther furiously curses Joan her under her own breath. But as Esther’s mental state begins to show clear improvement and she even manages to earn some privileges outside of the asylum, Joan’s progression takes an inverse course, starting with the loss of privileges and followed by a thawing of her exterior. Their rapport begins to soften, and soon Esther is able to tolerate Joan, which may signify that she is learning to become more familiar with her disease rather than trying to punish it. When Esther is figuratively and physically released from her state of confinement and begins to consider new options, even engaging in her first sexual experience, Joan quite literally fades into the background before completely being extinguished. The dull impact her death has on Esther perhaps demonstrates that Esther’s departure from mental illness is a process so subtle and so quiet that once it has lifted, one almost doesn't notice because the burden has been diminishing for a while on its own, as if trying to commit suicide. Esther's lack of compassion reveals she never really cared much for Joan, seeing her as little more than an uninvited companion she had become accustomed to.
The similarities between the two girls shows that Esther’s disease is an integral part of her -- it’s a replica of herself but not quite. Whether or not you choose to deliberate the symbolic nature of Joan’s character, the evolution of her presence and demise are extremely relevant to Esther’s story line in and outside the loony bin.