While you're adjusting Sona, maybe take the opportunity to introduce some scaling by rank to her E?

As it stands, Song of Celerity gains almost literally nothing by ranking it up. 1% movement speed. The smallest rank up bonus of any ability in the game. No change in cooldown or cost or duration or anything.

A lot of champions have a skill that they always max last, but ranking it up at least has some use. Like if I'm playing Annie and my team's frontline is lacking or nonexistent but the team has plenty of damage, I can rank up Molten Shield and do less damage but be better able to take hits. But for Sona, there is absolutely no choice; ranking up E past 1 point is just flat out wrong. Want to give your team more speed instead of more damage? Too bad, you can't.