Love how she didn't do a straight line across the back of her head then cut the zigzag pattern into the shaved part. Using the zigzag cut as the defining line between long hair and buzz cut and then continuing with that pattern in varying, fading lengths, makes it a softer transition from long hair to undercut. More feminine, less like a bowl cut.
Check out this entry from the Schwarzkopf Professional Canada contest - Create your colorful look using IGORA ROYAL Pearlescence hair color. Post your look & color formula, and tag @SKPpro #myIGORApearl. You & a guest could win a trip to LONDON, ENGLAND Prize value $8,700 - http://iconosquare.com/contests/myigorapearl/972583006778843872_189962199?langue=en#/media/detail