And suddenly, Cortana is left with a decision: keep pushing toward the goal or help her friend?

"Dammit!"

...It's not really much of a decision. She has no idea what other obstacles might surprise her on the way to Steel's resting place or how long it will take her to actually kill him and Yelena needs her help now and she is not going to let that asshole crack open another person's mind if she can help it.

So she changes trajectory, and runs toward Yelena instead of her original objective, reaching out to tear those wires from her arm with only minimal care for the damage she might do-a bit of bruising or dislocation is nothing compared to what will happen if they manage to burrow into her-and all the force an angry robot can muster.