She started her career in the late 1970s at the UK-based film production company Cucumber Studios which she founded with her partner - fellow director Rocky Morton. Jankel and Morton specialized in creating music videos, TV commercials and TV title sequences using a combination of live action, animation and the then emerging art of computer graphics. In this period the duo directed several music videos for performers including Rush ("The Enemy Within"), Elvis Costello ("Accidents Will Happen"), Talking Heads ("Blind"), Tom Tom Club ("Genius of Love", "Pleasure of Love", "Don't Say No"), Donald Fagen ("New Frontier") and Miles Davis ("Decoy").
In 1985, Jankel and Morton won an Emmy Award for their title sequence for the NBC show Friday Night Videos. And that same year their innovative TV commercial for the newly launched soft drink Quatro gained recognition at the British Television Advertising Awards.
In 2003, their 1978 music video for Elvis Costello's "Accidents Will Happen" was one of only 35 videos selected for inclusion in the Museum of Modern Art's prestigious "Golden Oldies Of Music Video" exhibition. Their music videos are found in the permanent collections of the Museum of Modern Art in New York City and at the Victoria & Albert Museum in London.
In 1984, Jankel and Morton co-authored a book titled Creative Computer Graphics that detailed the history of the craft and essayed its future.
Jankel co-created Max Headroom, a cult cyberpunk character that evolved into multiple TV productions and became very influential in science fiction TV and impacted popular culture in the 1980s. Jankel and Morton first created and directed The Max Talking Headroom Show - an entertainment program that featured comedic sequences, interviews conducted by the Headroom cyber-character and music videos. (Channel 4 - UK and HBO - US). This led to the TV film Max Headroom: 20 Minutes into the Future also directed by the duo. The TV film in turn inspired the ABC Max Headroom US TV series.
Subsequent to the success of Max Headroom, Jankel and Morton moved to Los Angeles and together directed D.O.A, a remake of the 1950 film of the same name, starring Meg Ryan and Dennis Quaid. The film received critical acclaim in the Washington Post and from film writers such as Roger Ebert who described it as "a witty and literate thriller".
Following D.O.A., Jankel and Morton directed the film, Super Mario Bros., a film based on the video game of the same name starring Bob Hoskins, John Leguizamo and Dennis Hopper. The film was set in a dark post-apocalyptic interpretation of the Mushroom Kingdom, as distinct from the colourful cartoonish setting of the game. It was panned by critics, receiving almost universally negative reviews. As of May 2013, review aggregator Rotten Tomatoes reports that 16% of critics gave positive reviews based on 32 reviews. The site's consensus states: "Despite flashy sets and special effects, Super Mario Bros. is too light on story and substance to be anything more than a novelty." Gene Siskel of the Chicago Tribune and Roger Ebert of the Chicago Sun-Times gave the film two thumbs down on the television program Siskel & Ebert At the Movies, and the film was on their list for one of the worst films of 1993. Michael Wilmington of the Los Angeles Times disapproved of the film's script. However, Hal Hinson of the Washington Post gave a positive review, praising the film for its spirit and later went on to say, "In short, it's a blast." Janet Maslin of The New York Times gave another positive review, but said that the film "doesn't have the jaunty hop-and-zap spirit of the Nintendo video game from which it takes – ahem – its inspiration."
Jankel became a director of TV commercials for clients such as Sealy, Coca-Cola, Bud Light, AOL, Bacardi, Hallmark and Greenpeace winning multiple advertising awards. Her Kiss spot for Hallmark was named "World’s Best-Humor Commercial", "Best Directed Commercial" and "Best of Show" at the International Broadcast Awards. She was also awarded the Gold Award for "Best TV Commercial Campaign" at the Worldfest REMI Awards.
In 2006, Jankel directed the 24-episode TV series Live From Abbey Road seen on Channel 4 in the UK and on the Sundance Channel in the US. - working with over 72 major musical artists including Paul Simon, Red Hot Chili Peppers, Dave Matthews, Norah Jones, Wynton Marsalis John Mayer and Dr. John.
In 2009 Jankel produced and directed an adaptation of the Carnegie and Whitbread award-winning novel Skellig by David Almond, a well received $5.3M Sky1 HD Easter Special feature-length production for TV broadcast and subsequent international theatrical distribution, starring Tim Roth, John Simm, Kelly Macdonald, Bill Milner and Skye Bennett.
In 2011 Jankel directed the 52 minute 3D show "Live On Air" shown on Sky3D Atlantic and Sky Arts, featuring the band Elbow, in rehearsal and performing at the 02 centre.