In Japanese there's a very clear distinction, because adjectives conjugate and sounds don't. Sounds also stand alone: it's possible and common to label a drink in a manga (cartoon) as "shuwa shuwa", while labeling it "fizzy" in English would be quite weird. The GP's daughter is really asking for "fizz juice", but again, that doesn't compute in English.

I've been learning Japanese for a long time as well, and I often hear this response by folks saying there's "no equivalent in Japanese" (aka the reverse).

Truth is you can communicate it, it's just communicated differently. Folks like to pretend there are mystical properties to a language, but reality isn't like that.

They said "outside of the underlying meaning," so I think they meant you can translate it, but there's no equivalent for the type of word?

Either way, I agree it was a poor example; I don't see any particular benefit to the Japanese word in this case.