"Operational requirements," Yelena suggests. "She wasn't your target. If she was on a SHIELD mission, she might have interfered."

A pause, and she smiles faintly, crooked and more than a little rueful. "If she wasn't on a SHIELD mission, she might have still interfered. She wanted to atone for what we are."

Natasha, she thinks, would have said what they were. Yelena has no such illusions.