... the similarity between her home situation and her vocal skill (having no voice) resonates strongly with us moderns, since it's a common idiom in both senses, but I wonder if we've uncovered another example of terms, and now idioms, drifting away from their antecedents.

Would Austen have recognized such a possible pun? would "have no voice" mean the same as "have no influence", as it does now?

I don't think a dictionary would give us such information; would a thesaurus? or something else?

...ok, Google found for me a quote from Abigail Adams, Austen's contemporary in America. This turns out to be a good, clean example of a quite possibly deliberate play on words.