-"You used to call home-life a hag-ridden dream, And you'd sigh, and you'd sock; but at present you seem To know not of megrims or melancho-ly!"-
The fourth stanza begins with the speaker again talking all about the difference between 'Melia's former and current life.
Back on the farm, she ('Melia) would complain that her home-life was a "hag-ridden dream."
A "hag" is just a witch, or an old crone—something like this.
To say that life is a "hag-ridden dream" is to say that, well, it is like a dream full of witches—scary, no good, unpleasant.
While this is one way to read this puzzling little phrase, there is a little more to explore. A long time ago, the phrase "hag-ridden" was used to describe a certain type of sleep disorder called sleep paralysis.
This is a condition where the sleeper feels like they're paralyzed, possessed, and being weighed down by something. (You can read a brief blurb about the condition here.)
So, what's the bottom line? 'Melia did not feel very good about her home-life.
She'd sigh, and sigh loudly ("sock"), and get all upset.
But now, she seems to have forgotten all about how unhappy she used to be.
She seems to know nothing about "megrims" (another dialect word, meaning "migraines" or even just "low spirits") or sadness.
So, is moving up to town and becoming a "ruined maid" the solution to all of life's "megrims"?
Well, maybe it's not quite that, but 'Melia can at least claim that she is a happier person now and that her life is a little better than it used to be, even though she's "ruined."
Even though 'Melia has chosen a less-than-conventional path, at least she's no longer suffering back home on the farm.
"True. One's pretty lively when ruined," said she.
And that's pretty much exactly what she says to her friend, our speaker.
People are pretty "lively" when they're ruined. They're happier, in better spirits, less depressed.
The irony here of course is that Melia seems anything but "lively."
She's almost like a robot, don't you think, with all those pre-programmed, generic responses?
We know we've said it before, but the idea bears repeating here.