Mello began making frequent appearances on television in the mid-90s, guesting on episodes of "7th Heaven" (The WB) and "Boy Meets World" (ABC) in 1996 and 1997, respectively. From 1997-1998 she had a regular role on the critically acclaimed ABC drama "Nothing Sacred". A provocative and somewhat controversial series about a renegade priest (Kevin Anderson), "Nothing Sacred" featured Mello as a receptionist in a Catholic church who deals with the emotional and spiritual fallout of an unplanned pregnancy and subsequent abortion. The series met an early demise despite its quality, and it was back to guest work for Mello, including a 1999 episode of "Zoe, Duncan, Jack & Jane", a New York-set teen sitcom on The WB.
1999 would turn out to be a banner year for Mello, who followed up forgettable roles in the direct-to-video releases "Infidelity" and "Overnight Delivery" (both 1998) with a supporting turn in the hit teen feature "She's All That" (1999). Playing Chandler Locklear, a stealthily sharp-tongued in-crowd member loyal to Uber-popular villainess Taylor (Jodi Lyn O'Keefe), Mello was surprisingly convincing as a catty high school student. She took a rather different role in "Popular" later that year, playing Lily Esposito, a tireless activist and one of the more outgoing and fearless members of the out-crowd. Down-to-earth and charming, with an energy more inspiring than annoying, Lily was an asset to the series due to Mello's skilled portrayal.
While "Popular" won a fiercely loyal audience and numerous accolades from various organizations advocating responsible programming, Mello continued to pursue film work in her free time, portraying the quirky Mars Girl in the independent comedy "Spanish Judges" (2000) and taking a supporting role in 2001's "Tortilla Soup", a Los Angeles-set Mexican-American remake of Ang Lee's "Eat Drink Man Woman".