Vigdis the War Maiden is a level 71 rare vrykul with approximately 14k health. She can be found in the eastern part of Howling Fjord just east of Nifflevar and north of the Explorer's League Outpost. I have indicated the area where she can be found in blue on the map below. She is one of three rares located in this zone. The other two are Perobas the Bloodthirster and King Pin.
Vigdis is part of the Northern Exposure and Frostbitten achievements. She drops Soul-Sealed Belt which is a level 70 bind on equip plate belt with a random enchant. Like other Northrend rares, she also drops Abandoned Adventurer's Satchel, which generally contains about 20 gold, a full stack of frostweave cloth, and often times a few crystallized elements. She also yields a decent amount of experience for leveling characters.
Although she patrols around on a proto-drake, she will only be found patrolling on the ground. You do not need to look for her in the air.
She also really has no special abilities to note, she doesn't hit hard at all. Any one leveling in the area that comes across her shouldn't have any trouble.