In such a fanfiction, Sarada might be in awe of Itachi. She could learn valuable ninja skills from him. Itachi might see Sarada's potential and offer her some advice on how to better control her Sharingan and improve her combat abilities.
One scenario could be that Itachi appears to Sarada in a sort of vision or time - warp situation. Sarada, being the curious and ambitious ninja she is, would surely ask Itachi a lot of questions. Itachi, with his calm and collected demeanor, would answer her as best he could. He might even tell her about Sasuke from his perspective, which could give Sarada a new understanding of her father. Their meeting could also lead to Sarada unlocking some hidden power within herself, perhaps related to the Uchiha bloodline in a way that she hadn't discovered before. This new power could then play a crucial role in the events of the Boruto series.