Why do we have two different contractions for the phrase “it is not,” namely, it isn’t and it’s not? (Three contractions if you count it ain’t).
Then again, no one ever expects the English language to be a model of efficiency and common sense, because it’sn’t.
The sentence “She is female” is odd.
One the one hand, it is utterly pointless: the only fact it conveys is already encoded in the first word of the sentence.
On the other hand, if you remove the last two words, it’s no longer a sentence and doesn’t convey any facts.