You are a tank, she is DPS. She shouldn't get agro at all or at worst only sometimes.
Depends on if you're running a Guardian or a Sentinel. If you're running a Sentinel, Kira shouldn't even BE there unless you're just going with Offense AS Defense strategy.
And if you're a Guardian, she IS your DPS when it comes to taking down the bad guys.
Kira and Jaesa serve the exact same purposes. DPS and Eye Candy.
All that said, Most pointless companion in the game HAS to be Skadge. Good lord, does he have to be dumb, ugly, AND evil??? Seriously, his DPS is in the toilet, and his Tanking ability is also nearly non-existent. Unless you're running a Healing spec, he goes down faster than Jill Kelly.
Blizz on the other hand fills the Tank role just fine, and he's a blast to take along on missions.