Level 42? Bah, don't worry about tanking until you are 60

Go full dps and have fun with her until then. You could even stay dps and have fun while leveling until 70, up to you though.
Link to the thread I have on prot. warrior links:
http://www.cgalliance.org/forums/showthread.php?t=20203
From best to worse threat: revenge, shield slam, sunder armor, mocking blow, heroic strike, thunder clap, hamstring, cleave and devastate.
Taken from one of the links listed in the linked thread above:
(A) Warrior
Most warrior abilities add a fixed amount of threat when they land successfully. The following table gives the raw values, i.e. before the modifiers from battle stance or defensive stance, and ignores the damage done by the abilities.
Sat - updated threat values courtesy Lavina from the EU forums
Sunder Armor (Rank 6).........301
Heroic Strike(Rank 11)........220 (estimated)
Revenge.(Rank 8)..............417
Shield Bash.(Rank 4)..........230
Shield Slam (Rank 6)..........307
Devastate.....................101
Thunder Clap..................+150% of damage done
Cleave (Rank 6)...............130 (threat split)
Demoralizing Shout.(Rank 7)...56 (threat split)
Battle Shout(Rank 8)..........69 (threat split)
Commanding Shout(Rank 1)......68 (threat split)
Spell Reflect.................0
Piercing Howl.................0
Concussion Blow...............0
Abilities noted as having "threat split" divide the generated threat amongs the targets affected. For example, if you perform Demoralizing Shout on two mobs, each mob gets 28 threat; on three mobs, each gets 18.7; etc.
As of patch (1.11.x), the behaviour of Taunt has been buffed slightly. It now does three things:
* Taunt debuff. The mob is forced to attack you for 3 seconds. Later taunts by other players override this.
* You are given threat equal to the mob's previous aggro target, permanently. Importantly, you won't necessarily get as much threat as the highest person on the mob's list, only as much as whoever is currently tanking it.
* You gain complete aggro on the mob at the instant you taunt. Usually you would need 10% more threat to gain aggro (see section 3), but a taunt now gives you instant aggro on the mob. Of course if other people are generating significant threat on the mob, they could exceed your threat by more than 10% before the taunt debuff wears off, and will gain aggro as soon as it does. There is no limit to the amount of threat you can gain from Taunt.
While Challenging Shout and Mocking Blow have a similar forced attack debuff to Taunt, they do not give the caster threat in the same way as Taunt, just fixed amounts.