Don't say:
Anne said to me, 'You're a foolish.

Say:
Anne said to me, 'You're foolish.

Note:
A fool or a foolish person doesn't mean an insane person, but one who acts thoughtlessly. We tend to use silly or stupid instead of fooKsh in modern usage. Fool is a noun, and requires the article when we use rt with the verb to be. foolish is an adjective, and can't be used wth the article after the verb to be.