She had lost the sexfight and had served as ‘slave’ for a week. On the final night of 'submission’ slave disobeyed Mistress and kept Mistress in orgasm far longer than Mistress had intended.
Mistress bellowed and came until she glowed in exertion and then flickered out like a candle. Slave left Mistress unconscious, and slave curled up in her slave-bed on the floor, knowing she was not permitted back on the mattress until tomorrow.
Mistress would know that she controlled a powerful slave girl for a week.