[mellonaut]

What an incredible feeling of self-agency and power it must be to be able to say “I am not dumb” after being called a dumb mute by everybody all your life. Amazing.

[Beltalowda]

At the time "dumb" mostly meant "not being able to speak" (mute); so she's saying "I can talk" and not "I'm not an idiot".

Kind of an interesting example how language changes.

[Ancapistani]

Ironically, "idiot" had a specific medical meaning as well. It basically meant "infantile".