Madame Serena is in South Qeynos at loc -38, 64, 2, south of the Mermaid's Lure, which is near the docks. She appears as a gipsy-style Human woman with an Enchanter pet (sword and shield). She doesn't respond to hails. Allakhazam says she has religious rhymes, though.
Give Madame Serena 5 plat or 50 gold.
"Fifty gold? You must want a rune of fortune. If you want another one, give fifty gold to Mizr N'Mar in the Neriak library."
You gain experience!!
You receive Rune of Fortune (which Identifies as "Rune of Fortune: Top").