"Where are you from, Elizabeth?"
Translation:Cò às a tha thu, Ealasaid?
As joannejoanne12 wrote, cò às means where from (is…)?, to add to that – the whole cò às a… part means where from is it that…?, and the sentence cò às a tha thu? means literally where from is it that you are?. The word a is called relative particle and it introduces a subordinate relative clause.
I’ve tried to explain such questions in many comments already, you can find some of them eg. in:
It was really just a general question word meaning who, what, which, where or even how and why in Old Irish. From the exact same source are the words cia and cà (they all kinda specialized in their meaning, eg. cà is only used for ‘where’ today), but they all continue different grammatical (or stressed or unstressed) forms of the same Old Irish pronoun. Here is its entry in Dictionary of the Irish Language (an Old and Middle Irish dictionary): http://dil.ie/8965