Sonya Cassidy character accent

I've just started this series and loving it. I realise the actress is British, but what is the accent of her character she plays (the DEA agent Susan Duffy)? It's lovely, but unfamiliar to me and seems uncommon in US TV shows/movies (or maybe I'm watching the wrong things)

Is it a good version of whatever regional accent it is meant to be? It's making me want to visit wherever she's supposed to be from!