What goes around comes around. In the final scene, we see that Eve's about to get her comeuppance in the person of a star-struck young fan whose brazen invasion of Eve's life puts Eve's own invasion of Margo's life to shame.
"Phoebe" (she says she "calls herself" that) has sneaked into Eve's hotel room on the night of the Sarah Siddons Award presentation. After a freaked-out Eve calms down, the girl gets busy tidying up the room and answering the door when Addison comes to deliver the award statuette that Eve left in the cab. "Phoebe" sucks up to Addison then doesn't even tell Eve that he was there—she says it was just the cab driver. Eve, lying exhausted in a chair, sounds as cynical and jaded as Margo.
As Eve rests in a chair, "Phoebe" picks up the stunning jacket that Eve was wearing at the ceremony. In an echo of an earlier scene with Eve and Margo's dress, she puts on the jacket, picks up the statuette, gazes at herself reflected infinitely in Eve's triple mirror, and graciously accepts the award and the adoration of her imaginary fans.
The scene sums up all the movie's themes: the quest for fame at all costs; pretense and manipulation; the fleeting nature of celebrity; the theater's search for the next, better, younger star; the inevitable disillusionment. The message? It's getting worse all the time. Looking in that mirror, we see that there are thousands of Phoebes out there, ready and willing to do anything and everything to be famous.