I talked about that a bit here, too.

I assume it’s also going to about her realizing her powers and what that means for her as a person. That’s what the Russos have said her journey is about. So far her footage frames her in a protective role, she has a plenty good reason to develop and expand her powers.

As far as Pietro–that story wrapped up with Ultron. His death was the final piece of Wanda’s narrative redemption. Besides Marvel Studios not wanting to deal with two Quicksilvers, Wanda’s character and relationships would be difficult to develop if he were still alive. Wanda had only 10 minutes of screentime (including non-speaking) in CW–a sizable chunk of that would have gone with Pietro, and that’s not the story they wanted to tell.

This is true of the comics too. To my recollection, Wanda and Pietro haven’t been on an ongoing together since a little after their Kooky Quartet days. They’ve had story arcs together, but not as ongoing teammates.

And as far as an in-universe reason goes:

1. By Infinity War it’s been 3-4 years.
2. People won’t talk about their dead loved ones to others who didn’t know them, and the Avengers didn’t really.
3. Again, Wanda doesn’t have that much screentime. Not a lot of space for her to bring up her dead brother.

Pietro may end up featuring in Wanda’s story in some capacity. But it wouldn’t be surprising to me at all if he won’t, and it would be a screenwriting mistake to bring him up beyond a short, meaningful mention unless they plan on it.