From Knackers yards , where horses were sent prior to going to the glue factory.
Declan
Not in Dublin it doesn’t. In that context it refers to members of the travelling community and is extremely pejorative. However, she still says “I am knackered” which then refers directly to the knackers yard as you say.
That’s true. But I’ve also heard girls in Dublin using “knacker” to mean “slut”, or at least that’s what I understood from the context.
Stinkpop, “she must have done” isn’t very Irish either. More likely it would just be
- Did Aoife go to the pub?
- She must have.
It must be a Dingle or Co. Kerry thing then, since they all say “must have done” around there. They love to leave out unnecessary words.
- Did Aoife go to the pub?
- She did
Sounds far more likely to me.
Not that particular conversation of course
but one that I did hear , was along the same lines
Q- Did Liam go to the pub
A -How the feck should I know , do I look like the beeb
I can’t be arrsed to keep ****** wereabouts all the time
Declan
Declan, nailed it 
in Brit knackers is testicles… 
Big Hairy Knackers!