In the comics, Yelena doesn't kill Clint. Their relationship is complex but not marked by such a violent act. There are various conflicts and resolutions, but not this one.
Love and romance are also likely themes. Writers may depict the development of romantic feelings between Yelena and Pieck. This could involve slow - burn romances where they gradually realize their feelings for each other, or perhaps more fast - paced love stories where they fall in love quickly due to some extraordinary circumstances. There could also be themes of sacrifice, where one of them is willing to sacrifice something for the other in the context of their relationship.
Yelena could bring a fresh perspective to the Avengers. Her skills as a Black Widow would be something they notice right away. She might start off being a bit stand - offish, but as she sees the Avengers' good intentions, she warms up. They could exchange combat techniques and strategies. And she might even teach them some of the more underhanded tactics she learned during her training.