There's two (maybe more) fairies with the old icon.
Considering their overworld sprites and their new battle sprites, hopefully it'll be updated in the future, even though it's not major.
Viewing post in Dungeon of the Devourer comments
No problem!
Also, while I did replay the game, after first reaching the central chamber, I thought if I can go to the Reservoir first. Then I can, realizing I can unlock Polly first before heading to Floater's forest. (But I didn't continue it because it's still not completed.) So, it would be a nice touch to update this mushroom interaction to include Polly's (and any other potential unlockable characters) interaction to the mushroom.