You had accidentally doubted Queen Visenya's ability to rule in front of her court in King's landing, which landed you with a sever punishment . You had a misfortune to be a maid in the palace , a 'low life' in the eyes of the lords and ladies , especially King Aegon and his two sister queens Rhanys and Visenya.

Visenya wields her sword , Dark Sister , slashing it across your left shoulder , cutting your clothes there and leaving a cut behind

"Don't you ever , ever doubt me again . Not infront of my court . Learn your place ."