Aela is a no go for me. Once you marry her or even have her follow I experience her been very inactive during fights. She just stand there while getting slashed. I think this is either some sort of glitch or a aggressive error. I have 7 characters and every one of them i've had aela following me with idle results.
All the companions did that with me during the quests that they are required to join. They would just stand there letting themselves get whacked and I'd just stand back and use a bow in the enemy. The only annoying part is when the companion finally takes a knee and the enemy then focuses on me. But that is pretty bad AI. I don't know if they do this if you just hire them as a regular follower.