The version that I sing (I can't remember who I got it from) contains the verses:

We had not been a-sailing not three weeks so many
When our ship it was becalm-ed sore
No way we made any

So they counted out black bullets, they numbered twice six and twenty
And the lot it fell upon this maid
On her and her baby

They've tied a kerchief round her eyes, they've tied it round so bravely
And they've cast the wrongdoer over the side
Both her and her baby.

Now it's see how she doth swim me boys and it's see how she doth swagger
And she will not stop her swimming
Till she comes nigh some harbour

Now it's see how the winds do blow me boys and how our ship is moving
That women was our cause of woe
And this is the proving.


I've assumed that the assumption about her swimming prowess, was that she was some sort of witch and therefore could not drown.