Mecchi was born in the third generation of her family that lived in San Francisco, California. She later received a Bachelor of Arts degree from the University of California, Berkeley. As she began to start her career, her aspirations to direct theater led her to study at the American Conservatory Theater, where her instructor, Second City alumnus Joy Carlin, was impressed with her writing and encouraged her to pursue it on a full-time basis. Her first work began when she wrote a series of children's programs for Nickelodeon such as By the Way. Mecchi's first network writing assignment was on the Emmy Award-winning Lily Tomlin special, Lily: Sold Out. Her later television credits also include Valerie,The Popcorn Kid, and My Sister Sam. Along with that, Mecchi researched and wrote a play drawn from 50 years of legendary newspaper columnist Herb Caen's witty observations of San Francisco. The play was "work-shopped" at the American Conservatory Theater and led Mecchi to edit two books of Caen writings, which were published in 1992 and 1993. Finally, Mecchi began her association with Disney in March 1992, when she wrote a 10-minute animated short called "Recycle Rex." That short film encouraged younger viewers to "recycle, reduce and reuse" waste materials. During the summer of 1992, Mecchi was brought on board to polish the script for The Lion King, which was pitched to her as "Bambi in Africa". Several months later, she was joined by Jonathan Roberts in the rewriting process of the screenplay. Together, both writers tackled the unresolved emotional issues in the script, and brought additional comedy with Timon, Pumbaa, and the hyenas. Following her work on The Lion King, she signed to co-write the screenplay of The Hunchback of Notre Dame and Hercules. Also, she re-teamed with Roger Allers to co-write the book for the musical adaptation of The Lion King, to which they were nominated a Tony Award for Best Book of a Musical. She would later re-team again with Allers to contribute additional screenplay material to The Lion King 1½. Meechi served as the co-screenwriter for the Pixar film, Brave, which was co-directed by Brenda Chapman. In June 2013, Chapman stated she and Mecchi were developing Rumblewick at DreamWorks Animation, which went unproduced. In November 2014, it was announced Mecchi was co-writing the screenplay for Lucasfilm's animated musical film, Strange Magic. That same year, she wrote the teleplay for NBC's Peter Pan Live!, in which she revised the characterization of Captain Hook.
