Fink was born in Houston, Texas, and has an older sister named Stephanie and two younger sisters named Amanda and Amy. She began acting at the age of four after playing the lead role in her school's holiday play. After moving to Los Angeles with her family, Ashley immersed herself in acting and began attending an Arts High School, where she began performing for large audiences as lead characters in adaptations including The Wizard of Oz (as the Lion) and You're a Good Man Charlie Brown (as Lucy). Fink has said that she was bullied in high school, but that she did not let it get to her.
Fink was cast as Lauren Zizes on the Fox television series Glee, making her initial appearance in the first season episode "Wheels" as a champion high school wrestler and cheerleader tryout candidate. She made irregular appearances until the ninth episode of the second season, "Special Education", when she was tapped to become the glee club's twelfth member after Kurt Hummel (Chris Colfer) transferred to another school. Fink has said that "I was obsessed with Glee before I was a big part of it and I’ve steadily been on it for a while. When I got the script [where I joined the glee club] I texted Chris Colfer and said, 'I think I just joined the Glee club?' I didn’t quite believe it at first, I thought I was getting 'Punk'd.'" She remained in the glee club for the rest of the season, and was given storylines of her own. Critics have responded well to her portrayal of Lauren. Robert Canning of IGN praised Fink's performance as Lauren, and said of the "Silly Love Songs" episode where Puck (Mark Salling) falls in love with her, "I can't decide if I want to root for this couple, but I certainly know I'm going to be rooting for Lauren." Fink received several positive reviews for her performance in "Comeback", in which she sang her first—and so far only—solo on the show, a cover of "I Know What Boys Like" by The Waitresses. The song was released as a single, but it did not chart, nor was it included on a Glee soundtrack album. While Todd VanDerWerff of The A.V. Club found Lauren's relationship with Puck in "Comeback" "a lot less assured" than in the previous episode, "Silly Love Songs", Sandra Gonzalez of Entertainment Weekly deemed their scenes "as endearing as they are unrealistic".CNN's Lisa Respers France commented that she was beginning to really like Lauren, and noted that "for me Lauren represents how Ryan Murphy is able to take the concept of the outcast, flip it on its ear and shove it back in our faces with a side order of fabulousness." Despite the positive critical response, Fink's character quit the glee club in the series season 3 premiere, "The Purple Piano Project". While she appeared in a non-speaking capacity in the Season 3 episode "Asian F" and series creator Murphy alluded to her character's reentry into the plot through interactions with Kurt Hummel, Fink confirmed later that season that she would not be returning to the series. However, she subsequently reprised her role in the season 4 episode "Sadie Hawkins".