Susin got her start feeding cast and crew muffins and bologna sandwiches on the award-winning television series, Degrassi Junior High. They hated her food (a fact that's memorialized forever in a poem the cast wrote: "An ode to Susin, the Bran Muffin Queen, we eat them, we die, then we turn green"). Luckily for Susin, however, they saw a spark in a spec script she wrote. Susin went on to pen 16 episodes of Degrassi Junior High and Degrassi High. She also got her first crack at novel writing when she was asked to write Shane, one of the books in the Degrassi series. She went on to write three more: Wheels, Snake and Melanie. She loved writing in book form, and vowed that one day she would write an original young adult novel.

But the TV world beckoned, and over the next number of years Nielsen wrote for and executive story-edited on many well-received TV series, including Ready or Not, Madison, The Adventures of Shirley Holmes, Edgemont, Heartland and the animated series, What About Mimi and Braceface. She also co-created the pre-school series, Franny's Feet. More recently she co-created the critically acclaimed series Robson Arms, acting as head writer and showrunner for three successful seasons. She also adapted Alice, I Think for television, a half-hour comedy series based on the best-selling novels by Susan Juby.

In between the TV work she found time to write three children's books: Hank and Fergus (winner of the Mr. Christie's Silver Medal Award), Mormor Moves In (both published by Orca), and The Magic Beads (published by Simply Read).

Finally, in 2006, she fulfilled her vow from years earlier and wrote her first wholly original young adult novel, Word Nerd. It was published in fall 2008 by Tundra Books.  Her second novel, Dear George Clooney: Please Marry My Mom was published by Tundra in fall 2010. Her latest novel, The Reluctant Journal of Henry K. Larsen, was published in fall 2012.

Susin lives in Vancouver with her husband, son, and, hopefully soon, two, count 'em two, cats. (PS: She got the two cats: Erwin Schroedinger and Emily Bronte).