Let's consider the facts.
- She's Touko's best friend, and has an understanding of sorts with Yuu, so it's possible that one of them may end up talking to her.
- Since she has a first-hand view of how awkward things are between the two of them during Student Council sessions, it's possible she'll end up demanding to know what's going on.
- She has experience dealing with heartbreak- both her senpai dumping her fairly abruptly and her feelings for Touko going unrequited- so perhaps she can help Yuu understand that it's perfectly normal to feel the way she does about Touko's apparent rejection of her.
- As for Touko, perhaps realizing that Sayaka has loved her all along and still continued to be her friend can perhaps help her get over her desire not to be loved.
The only potential obstacle may be Sayaka's apparent jealousy of Yuu's closeness with Touko, but on the other hand, Sayaka seems to have accepted that her love for Touko is unrequited, and chosen not to confess.