God I hope they don't retcon TWS here, pull some "Natasha got amnesia or had her mind wiped sometime prior to the MCU movies we've seen!" crap where she and Bucky knew one another.
Just keep it to how it is, she crossed paths with him once, he shot her, she could never track him down afterward. They don't need to be Commie colleagues like in the books. Doesn't work with her age in the movies anyway.