Shes kinda near the docks. Like where to two aqua gobs camps are. Heading towards the docks on the road you will see a passage to the left of you. Shes somewhere in there. Ran into her yesterday and killed her. lvl 10 btw. so shes not hard.
Margyl's Tongue is used for the paladin armor quest. I believe it is for the guantlets. Check quests for North Kaladim for more info. They are called Underfoot Defenders armor quests.
She is one of the Butcherblock bandits. killing her, or any of the Butcherblock bandits, gives positive faction with Miners Guild 628, or whatever number the Dwarf Rogues Guild is, as well as Stormguard. You can check your faction progress by conning the two guards nearby at the little guardhouse, they have the same faction as the Rogues, not Stormguard like the other dwarf guards.