You would say "I already know you don't", to echo "don't feel comfortable".
Both proverbs would fit, in a loose sense; but I'm not sure that either is a particularly likely continuation.
The "bridges" proverb expresses a warning, as if Kate were about to confront Mrs K in some way; but that's not explicit in the context.
"One man's meat" is usually used as a gentle reminder that the addressee's opinions are subjective, or a reflection on a situation as a whole, where there are evidently conflicting parties; but in the dialogue here, it seems out of place, since the speaker seems quite sympathetic to Kate.
That said, I can't think of a proverb that would fit the situation exactly! Maybe another member will know of one.
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