To my ear the Beatles version sounds fine and your version doesn't, sorry. However, you do need to be careful if you take the language in pop songs as correct; artists sometimes ignore grammar if it sounds better (or maybe the artist doesn't know any better!) 'Eight Days a Week' anyone? Exams are different from art and real life, I'm afraid. Good luck!

While the person above me is correct, it is important to remember that a lot of the time in creative works (poetry, music, books) correct grammar is not 100% percent necessary. Especially in music because syntax and rhyming are important!

I believe the line you quote is perfectly correct English. I would punctuate it as "Why she had to go, I don't know--she wouldn't say." "Why she had to go" is correct grammar if you interpret it as "Her reason for leaving." "Her reason for leaving, I don't know--she wouldn't say." "I don't know her reason for leaving--she wouldn't say." I agree that it _could_ also be bad English, if you imagine that it is something like "Now why she hadda done go? For why she do that thing?" But not in this song, because the other words of the song are in standard English. And, yes, song lyrics are unreliable. Songwriters often bend grammar for the sake of the rhythm and rhyme. Furthermore, they sometimes write poetry that evokes a mood without having a clear logical meaning. The Beatles range all over the spectrum. Consider: I am the eggman They are the eggmen I am the walrus Goo goo g' joob!

Paul McCartney wasn't asking a question in that passage. He is saying that he doesn't know why she had to go because she wouldn't say. The first two phrases sound more natural if you reverse the order: "I don't know why she had to go." Such is the nature of poetry.

You're right (for the reason you mentioned) and the sentence is wrong. Here are two possible correct versions: a) Why did she have to go? I don't know - she wouldn't say. b) Why she had to go is something (that) I don't know - she wouldn't say.