Are all these forms acceptable?

She is a Pole/ _Polish.
She is Spanish/a Spaniard.
She is a Dane/a Dutch/a Dutchwoman.
She is Swedish.
She Danish.
She is a Turk/Turkish.
She is /a /Finnish.

She is _ Dutch/a Dutchwoman.
She is Swedish / a Swede.
She Danish/ a Dane.
She is a Finn / _ Finnish.

The others are fine.
The best usage would be:

She's Polish.

She's Spanish.

She's Dutch.

She's Swedish.

She's Danish.

She's Turkish.

She's Finnish.
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I see no advantage for 'She's Finnish' over 'She's a Finn'. What is your support for 'best usage', Anonymous?
One problem with the "She's an (x)" usage is that it extends naturally into more unpleasant uses like "She's a Jew" [which is not inherently offensive but is touchy depending on context], while e.g. "She's Jewish" carries no negative connotations.
I agree with CSnyder. When someone says "She's a Pole" there is a connotation that nationality is the most important thing about that person, or that Polish is what she is. When someone says "She's Polish" the connotation is that her nationality is a characteristic, her heritage is a part of who she is.
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I fail to feel the nuances. While 'Jew' may be intended as a derogation by some bigots, 'Polish joke' is intended as such by others. Some people may not personally like the unique demonyms that are particularly prevalent in Europe (Dane, Swede, Briton, Spaniard), I have seen no grammar that demonizes the terms out of hand, or in fact treats them in any way other than as alternatives that sometimes appear in different contexts (for instance, the adjectival form is much preferred for the plural).