My question is not whether the correct grammar is either "She has just had a baby" or "She just had a baby". I am aware that the official grammar is "She has just had a baby". But in a way that sentence sounds wrong. It is correct in the meaning that it follows the grammar rules and guidelines. However, when you "have just had a baby", somewhere in my mind it is as if that person is still having that baby. As in, the birth is still going on. But when you say "She just had a baby", the birth is done. It's finished. Which is (hopefully) the case.
So my question is actually more of a wiki-question expecting opinions on the implementation rather than a question expecting a valid and factual answer.