Is a young version of Greta. Rosie, like Greta, works in the Looking Glass, and they both have dark hair and brown eyes.
Rosie is the person behind Sun in "Namaste". The person shown is similar to her with the long hair and 70's styled t-shirt. Additionally she is credited in the episode on the official ABC Press Release.
If Rosie is a nurse, she should work at The Staff. So far, The Looking Glass has been revealed to a) jam transmissions (a la Ben) or b) guide the sub. A nurse would have nothing to do with either.