I’m going to try a cleric/rogue for my next playthrough. You don’t need darkness really. A rogue would fit her shady nature. Sneak attack works with invoke duplicity. Dual wield would allow the use of off-hand after invoke duplicity. Blessing of the trickster allows for an ally to sneak with her. Likewise pass without trace. Mirror image helps for fighting in melee. Blindness or hold person are great with sneak attack. Silence is also a sneaky spell.
Medium armors are good with average to high dexterity, and become even better in act 3.
Items would be those of a rogue but with a medium armor. Assassin would probably be my subclass.