[5][6] She attended Bard College and studied illustration and cartooning at the School of Visual Arts (SVA) in New York City,[5] where she graduated in 2014.

"[16][17] Additionally, Aster's tomboy friend,[18][19] Charlotte "Charlie," who has two dads, is described as not conforming to gender norms, even by the book's publisher, Scholastic.

[23] Paste described Ostertag's character design as "deft and varied, with a thick, dark line that resembles that of Faith Erin Hicks", noting that she "mostly uses her figures' eyes and their body language to convey emotions.

[25] Additionally, Erica Friedman of Yuricon, a long time fan of Ostertag, praised her work, How the Best Hunter in the Village Met Her Death, calling it a tale that will resonate with those "who have come through their own dark forests and transformed into their true selves.

[27][a] She noted that it is somewhat based on her experience spending summers at Wilneff Island in Nova Scotia as a kid and called the book her "first serious foray" into the romance genre.

[32] In September 2024, Ostertag announced that Neon Galaxy, a series set "in the distant future," was not moving forward at Disney, noting that it had been cancelled a few months prior despite production work for four and a half years and positive response from "kids who saw materials in early demographic testing" and songs by Betty Who.

"[33] From July to September 2020, Ostertag published a The Lord of the Rings fanfiction titled "In All the Ways There Were" which shipped Frodo Baggins and Samwise "Sam" Gamgee together, a story which became relatively popular.

She also told TheGamer that she is ok with making "people uncomfortable" with her stories, and expressed a desire to have more "butch lesbians...fat characters...visibly trans characters...[and] super femme gay men" in her stories who are just "hanging out and existing" and said that despite abundance for queer media presently, people involved in productions for big companies are "afraid of getting it wrong".

[46] Ostertag is also a member of the Democratic Socialists of America, and has illustrated a campaign poster for Los Angeles City Councilmember Nithya Raman.