Teach Rosa Var Attre to fence, witcher-style.
The Witcher 3: Fencing Lessons
This quest is available one day after you complete main quest Broken Flowers, part of Act One: Novigrad, if you agree to keep teaching Rosa.
Visit the Var Atre residence and inform the guard of the purpose of your visit in order to be directed to Temple Bridge. Off you trot.
Beat Rosa up and she'll beg a moment's discretion to adjust her undergarment. As you turn a gentlemanly back, she legs it. Hunt her down using your Witcher Senses to find her trail, ending up in an altercation outside the Seven Cats Inn.
You can resolve this situation by telling the fellows to go away and starting a fight; offering them 50 crowns to go away; or using Axii level two to convince them to go away.
In any case, once they've left Rosa reveals she really is a spoiled Nilfgaardian brat. Say whatever you like to her as the quest concludes.