She is initially an ally to series protagonists Sam and Dean Winchester as well as to Castiel, but becomes an antagonist in her final episode when her method for averting the Apocalypse in the fifth season pits her against them.

Although McNiven received general praise for her debut and chemistry with actor Jensen Ackles, who portrays Dean, critics thought that the character lacked direction in her later appearances and questioned her ultimate betrayal.

Demons attempt to capture her in "I Know What You Did Last Summer" when they realize that the voices in her head are actually communications between angels, but Anna defends herself in a burst of telekinetic power and makes her escape from the hospital.

"[9] Actress Julie McNiven, on the other hand, felt that angels do have the potential for emotions—both she and actor Misha Collins agreed that "there's something more there [between Anna and Castiel] than just being co-workers"—but are forced to suppress them by the militant atmosphere of Heaven.

"[12] McNiven only "felt weak" in the role of Anna when she was a "confused mental patient" whose "whole life just completely fell to pieces," with the character becoming "very strong" upon discovering the truth.

"[12][14] Deciding to return to her angelic form is a "big struggle" for the character, but McNiven believed that the restored Anna eventually "found a middle ground" because being on the run allowed her to make her own choices and thus feel human.

"[16] Production envisioned Anna as "this one beautiful, frightened girl," and series creator Eric Kripke said that McNiven "blew [them] away with how likeable, vulnerable, and intelligent she made [her].

"[17] The actress auditioned for the role of a mental patient, unaware of the character's angelic nature, and only learned the truth when later asked to read scenes from "Heaven and Hell.

"[12][18] Considering herself to still be in the early stages of her career, McNiven felt like she "could really bite into [the] role," and was especially pleased that her two-part debut provided the character with "an arc with a beginning, middle and an end.

[12] Though the character disappears at the end of "Heaven and Hell" once she becomes an angel again, Gamble assured fans that the writers were planning for Anna to reappear "soon" in the fourth season, which came to fruition in the episode "On the Head of a Pin.

[12] Brown as well as Kate Lloyd of The Official Supernatural Magazine noted that the character shares her surname with John Milton, author of the epic poem Paradise Lost.

[26] Steenbergen and Charles agreed with The San Diego Union-Tribune's Karla Peterson that McNiven shared a "low-key, sympathetic chemistry that worked beautifully" with actor Jensen Ackles, who plays Dean.

[31][32] When Anna is captured by the angels in "When the Levee Breaks," Peterson commented that "if...she is out of the picture, you will hear no complaints from me," opining that McNiven was part of a larger trend of "weak" casting for Supernatural's female characters.

"[36] Although Maureen Ryan of the Chicago Tribune liked Anna in the fourth season, she criticized the character in "The Song Remains the Same" for "wasting time and randomly throwing [the Winchesters] around" rather than quickly killing them.

"[37] Contrary to critical reception, McNiven believed that people did not initially like the character—notably because they "maybe didn't like the idea that an angel could fall" and saw her as "really selfish"—but over time saw her as a "strong female power character".