Speaking of Rachel Weisz, for all the talk about Yelena and Alexei's relationship she doesn't seem to care all that much about her "Mom" or mention her. Alexei doesn't seem to want to reconnect with his "wife" either.
I think it's ok in this case as she doesn't feature in the movie but Alexei does. Introducing her in name but not in person would just needlessly confuse people even though i figure they left in good terms after Black Widow.
We also see why Alexei cut her out as he was dealing with his own problems and depressions feeding back into the narrative of the whole movie. It would have been hard coming up with a realistic reason why her mom would cut contact and they already cut the shame rooms for the other characters in the movie.