Opposite/Negation of phrases

Solution 1:

As you clarify in comments, we'll assume that all candidate negations have been determined.

Syntactically, if you negate an adjective-noun phrase, @BillJ's comment makes sense: negate the adjective. So the opposite of short woman is tall woman. This becomes problematic when you have multiple adjectives - e.g. tall, famous woman, where your question repeats with respect to the multiple adjectives. If we want the (unique) semantic opposite to a phrase, we need more information.

To derive an opposite or negation, you need to specify what quality is being opposed or negated.

Here are some examples:

• take one of the ideas in @Deonyi's comment: if the quality is plurality (singular vs plural), then the opposite of short woman is short women;
• if the quality is the adjective, then the opposite of short woman is tall woman;
• if the quality is gender, then the opposite of short woman is short man; and
• if the quality is age (adult vs child), then the opposite of short woman is short girl, etc.

Once you specify the quality being negated, whether explicitly or via the context, the negation follows immediately. Without that specification, there are no grounds on which to judge any candidate negation correct.