[@Altered Tundra] It's rather obvious at this stage in the game that Natasha is never acting out of her own self interest. She's either working for Fury or at the request of Fury to the point that she helped Cap become a fugitive when SHIELD was compromised because the person she was loyal to most was dead at that point, which she wasn't aware was a deception. Now with SHIELD being whatever the hell it is in the movies now, she was allied with the Avengers at the end of Ultron. 

Chances are pretty high at this point that whatever Natasha does will in some way benefit the team. Widow knows the value in manipulation and subterfuge because literally everyone else would prefer just going smashy smashy shooty shieldy to get things done. 

Whose USB was it that was a plot point in Winter Soldier and who was it that got it? Widow.