From what I remember, Rosie doesn't meet the two otherworldly ladies in the ruins of Ludd. Dorcas reminisces about seeing bodies crucified along the highway to Ludd, so there is definitely a connection to the Dark Tower, and the ladies speak in a dialect similar to Roland's world, but the location they meet Rosie (depicted by her painting) is rural.
I guess it could be in the ground of future Ludd long after it was leveled and grown over but this is not mentioned.
I really enjoyed the novel. Apparently King wasn't keen on it. He felt it was 'trying too hard: (if I remember correctly), but I felt it was a novel with a lot of heart and compassion and I loved the magical world hopping stuff. It reminded me of how the kids crossed worlds in Chronicles of Narnia: Voyage of the Dawntreader (a picture was a portal, there too.)
It was the book that got me into the Dark Tower Series too.
