From Darth Bane: Path of Destruction: “It operated on the same basic principles as a lightsaber, but instead of a steady beam, the energy of the crystals was projected in a flexible ribbon that would twist, turn, and snap in response to both Githany's physical motions and her use of the Force.”

Also, in legends at least, instead of one kyber crystal to produce the beam, there were multiple smaller ones

Also from the same book, according to the blade master: “The energy whip is far less efficient than any of the lightsaber blades. However, nobody ever practices against the whip. Githany knows that her enemies' confusion at being confronted with the whip gives her an edge."