As far as I can tell, there's about a 0% chance their feelings aren't mutual.
Well yes, but maybe not instantly. My guess would be that Yuzu is about as "in love" with Minami as Minami was in love with Yuzu 48 hours earlier. She loves her, but hasn't realized that it'd be cool if it were romantic instead of platonic. I wouldn't mind being wrong and you being right in the slightest, though.
Barring conveniently inconvenient events that prevent either Minami from coming forward about it or Yuzu from responding, I see some rather quick development for this first step.
I'd love it if Yuzu weren't instantly "realizing a huge crush on Minami", but instead if she was plainly open to the idea and willing to see where that road goes. Now where have I seen that kind of dynamic before... (even if it was anything but childhood friends there).
I myself suspect she's just similarly afraid of ruining their friendship, pretty sure she rejected the guy due to her feelings for Minami as well - possibly because she's always known how she feels, possibly due to a similar reaction and realization after the confession.