Even if Val wasn't the female Nick Fury (don't be surprised if they have romantic history in the MCU), the legend of the blip and how it was resolved is not a secret. Her running point for clandestine operations means she has even more details than the average person about everything.
Yelena does need a reason. She has been spending more of her time freeing her fellow hired assasins than taking kill orders. Approaching her like a straight up weapon you can point at anybody for any reason is the kind of shyt she has been rescuing her sisters from. The only way to point her in the direction you want is to make it emotionally appealing in the context of her real mission.
Love it or hate it Black Widow has a lot of feminist undertones. Look at the scene where she's rescuing her sister from...nothing. She's like what you think some big bad man has me trapped here? I been getting it how I live..choosing to be the villan, unlike Nat.
Clint, the last person (a man) to see her sister alive is a proxy for men in general. Initially using Kate to get to Clint, she actually comes to see her like a sister. If she's been keeping close tabs on her the duration of the show, she already KNOWS that Clint isn't palling around with Kate for the fukk of it. He could have easily ler her hold her own nuts and went to have Christmas with his family.
Now is that a missing story beat? It didn't feel like it to me but I can see that argument. A quick scene of her survailing Kate (and Clint) before popping up in her hideout could have made it more clear.