If you're looking to tank with a rogue (I'm not, I tried a single quest area on Nightmare with Isabela tanking and it was... ... a nightmare), I would say rival Isabela is probably your best choice. Rivalry gives her a 10% dodge bonus, the Swashbuckler skill tree would give her +10 to defense (per enemy) from Savvy and Across the Bow is a single target taunt that (according to the skill description) can't be resisted. And then you could focus on the Scoundrel skill tree for further aggro control.
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