World-of-warcraft – How to make topfit work with legion’s “dual-wield” artifact weapons

It doesn't matter more for the off-hand than for the main-hand. You will still use the highest median damage weapon in main hand. Median damage is (Max+Min)/2, if you use median damage you can ignore speed because quicker weapons will automatically have a lower median damage.

And since you are dual wielding you will have a penality to hit (and damage) to your off hand. So your priority should be your main hand because of special abilities (opposed to auto attacks). As for the off-hand you will want slow weapons (and high median damage) because unlike rogue who will want to apply quickly poisons you will want to do more damage with each hit.

Higher median damage is always better for a death knight.

Enhancement Shamans are designed to dual-wield for maximum damage. If you aren't using an offhand weapon, you won't be getting your full damage output.

The fundamental truth is that if you're looking to take the least damage, don't go with the shield -- you'll take less damage overall if you kill things faster. Less damage done means more hits taken, which means the armor bonus of the shield is moot, as you take approximately the same damage either way.

And I hope she's not trying to level on mobs 3 levels higher than her. Stick with yellow or green mobs -- they're easier, you miss them less, and, again, you'll net higher xp/hour because you'll kill them faster than you would the orange mobs.