I think I've heard her say ble as well, which I had previously thought was "southern".
All less clear-cut than I thought obviously
I did find it interesting when David says something in "southern" and Rhys reacts in "northern" as if David had said it in "northern" as well.
Two places I remember are when they were in the hotel downstairs in the bar and David asked him something with Wyt ti'n moyn ...? and Rhys responded with Nac oes!, which is apparently not uncommon in the north as a response to Ti isio ...? based on the fact that that construction originated in something like Oes isio ... arnat ti? "is the need/want of ... on you? = do you want ...?* -- and the other in the recent episode where David twice said, on separate occasions, Alla i ddim ... and Rhys responded with Na fedri.