For all I know most mute people can hum and make noise. In Marci's case I don't think she can. There are factors to consider when can a mute make a noise. Are her vocal chords damaged to where she cannot speak at all? Or even make noise? Basically— can they vibrate? If not, then humming and moaning is impossible. Whistling doesn’t require vocal vibrations so that explains the voice line. But I do find some lines really ridiculous and shall I say, sounded stupid to me, Like, I've never seen a mute person irl that whistles when they laugh. most cases, a complete mute will just make faces, clap their hands or literally slapping the table! (my cousin is a mute)
To be more realistic, I do think playing a flute or other small instrument to mimic her laugh and "thanks" is alot better. I mean. just like how taunt works. I really do think that's one way to improve her "voice line". but what do u guys think?