You know what Soraka needs to make her more viable in higher ELO? Some better form of CC. So, with that in mind, how about renaming her E to "Banana Peel" and changing it to a VERY short range (so she has to get into Starcall range to use it) trap that, when stepped on by an enemy champion, knocks them up ("trips") for a duration of Riot's choosing?
It could also be a skillshot knock-up or stun like her E already is, but I feel like a trap would take more skill. ALSO, her traps would not be able to be used as wards as Soraka almost always buys sightstone anyway.
To make said banana trap not entirely overpowered, they wouldn't need to be invisible (it's a banana for God's sake).
I'll leave y'all to discuss whether or not it'd be best for her to be able to plant more than one banana at once, but I think if it was the same cooldown as her current E or a little bit longer, there are ways to make it fair.
In short, I believe this ability fits her banana theme all the better! I mean, for Pete's sake, she already says in her /joke dialogue, "Yes, that IS a banana!" Her throwing out a banana peel could practically be the same animation (but maybe not as perdy and sparkly as the basic attack lol).
Anywho, before you think of all the ways this idea could be wrong, please think of how it could benefit FIRST. Don't be a negative Nancy. Thanks!