Rosa var Attre was the twin sister of Edna var Attre and daughter of Henry var Attre, a Nilfgaardian Ambassador. Due to her father's position and title, she and her sister moved a lot, going wherever their father's job took them and, in 1272 during the third Northern War, they ended up in Novigrad.
She was an avid fencer and possessed a fair amount of skill as she took lessons from soldiers and professional swordsmen, though she mainly took up fencing due to boredom, having no friends in Novigrad, and didn't like attending banquets.
While in Novigrad, her father hired Dandelion as a rhetoric tutor for his daughters, though he wasn't successful and, unbeknownst to the girls, was actually using some of the lessons to learn what they knew of Margrave Henckel. To top it off, her sister Edna, who loved to cause mischief as much as Rosa loved fencing, wrote up love letters and signed them as "Rosa" and sent to Dandelion, causing awkward scenarios between them until Rosa made it clear she wasn't interested in the "old bard".
Later on, when Geralt started to investigate into what happened to Dandelion, he met Rosa and Edna and questioned them on the bard, with the sisters revealing his odd behavior during the rhetoric lessons and him singing about Priscilla.
If Geralt agrees to give her lessons: The fencing lesson Geralt had given her while searching for Dandelion had thrilled her to the core and left her asking the witcher if they could meet again for a repeat, to which Geralt agreed.
Once they were done with their lesson and the witcher was supposed to take her back home, she faked having to re-adjust her corset, getting Geralt to look away for a moment, and slipped off, wanting to go have some fun.
However, she didn't make it very far and ran into some low lives near the Seven Cats Inn who verbally threatened her until the witcher appeared and got her out of the tight spot. In that instant though she showed a darker side of herself, almost whimsically ok with killing Nordlings and anyone who so much as insulted her. Geralt then sent her directly home after it became clear the two didn't see eye to eye on matters.