I guess you've forgotten the scene at the farmhouse in Age of Ultron where Nat asked about "little Natasha" and Laura admits that he's "little Nathaniel" (to which Nat says "Traitor" to Laura's belly).
Oh, damn, I had forgotten about that (at least I think I knew about that, it does sound familiar). It's a shame she didn't get the role, even if Meng'er Zhang did a terrific job in the role.
That said, that wouldn't have been the first time there's been double casting between the films and the pre-Disney+ shows, most notably Enver Gjokaj as Daniel Sousa in Agent Carter and Agents of SHIELD and a cop in The Avengers. I'm pretty sure there are other examples.