The little girl is the ghost inside the Ghost Lantern, nominally under Yang Xiao's command, but the ultimate interpretation lies in the hands of the good sister in a drama robe.
Without saying a word, the lantern girl and the old man who looked like a butler, with their deathly stone faces, began to... act in front of Yang Xiao.
Well... it must be acting. The old man hid in the mist, his figure murky, while the little girl, holding a piece of Joss Paper Money, hopped over and tried to stick the paper onto the old man's body, again and again if the first attempt failed, and thrice if twice didn't work...
After watching for a long while, Yang Xiao finally saw the trick, but it also scared him pale. He understood what the good sister wanted: she wanted him to stick the Paper Money from the Opera Robe Shadow Garment onto that withered old ghost!
The good sister had taken a liking to the other's abilities and wanted him to snatch that ghost.