I think Maribel gave her some coffee and Kyouko have sort of allergic reaction.
In my college was teacher who had coffee machine in his cabinet - he drink quality and strong coffee. When he drink a cup of that, his voice change from smooth tenor to quiet and husky voice for some time.
Considering Kyouko is "voice yokai" - losing voice is critical for her.
I think Maribel gave her some coffee and Kyouko have sort of allergic reaction.
In my college was teacher who had coffee machine in his cabinet - he drink quality and strong coffee. When he drink a cup of that, his voice change from smooth tenor to quiet and husky voice for some time.
Considering Kyouko is "voice yokai" - losing voice is critical for her.
That sounds quite reasonable... though it's probably much simpler to just say she gulped it too fast and is choking.