While re-reading GoT I was at the last Arya chapter and found the following passage.

"A red-haired whore in a wisp of painted silk pushed open a secondstory window. 'Is it the boy king that's died now?' she shouted down, leaning out over the street. (...) As she laughed, a naked man slid his arms around her from behind, biting her neck and rubbing the heavy white breasts that hung loose beneath her shift."

And a bit more.
This does sound like Ros to me: red hair and heavy white breats. Though she's given a much bigger role in the series, no doubt, but maybe this inspired them to pick someone that looks the way she does?