differences - gone vs. due (words refering to pregnancy)

You hear sentences like "How far gone is she?" Or "When is she due?" Used to talk about pregnancy...

A few days ago one of my collegues used the sentence "How long is she due?" and insisted that it's grammatically correct and means just the same as "How far gone is she?"

But it really doesn't make sense to me. I'd like to know what native speakers of English think about its grammaticality!

And my main question is, what's the difference between "How far gone is she?" And "When is she due?" ?!

Is it that the former asks about the amount of time passed and she's been pregnant and the latter to the remaining amount of time before giving birth to a baby?

Thank you in advance

Answer

Is it that the former (gone) asks about the amount of time passed and she's been pregnant and the latter (due) to the remaining amount of time before giving birth to a baby?

Yes, that's correct. When a pregnant woman presents to a caregiver, she's given an official due date (EDC or estimated date of confinement), so any question about her due date is usually when or what: when is she due/what's her due date? Sometimes how long until her due date. It addresses when or how much time is left in her pregnancy.

How far along is she addresses the amount of time she's been pregnant. How far is she (into her pregnancy)/how far gone (that sounds like an incurable illness to me) is she/how long has it been are all used.

I've never heard long and due used together except as above. It seems to me (AmE) to be a contradiction, and I wouldn't quite know how to answer that.

"How long is she due?" seems to require the answer, "Nine months" to me.