At the sight of her Tripitaka sprang up at once and, palms joined at his breast, said, "Lady Bodhisattva, where is your honoured home?

Watch how fast the doubt evaporates. One look, and he is on his feet with 合掌當胸 — palms together at the chest, the formal monastic greeting, 當 read dāng, "at, against". 府上 is honorific for another person's home, nearer "your residence" than "your place". He is being courteous, and courtesy is already halfway to belief.

"Of what family are you?

Four characters of polite enquiry. 甚 is shén, "what".

"And with what vow in your heart do you come here to feed monks?"

願心 (yuàn xīn) is a vow made in the heart, the promise offered to a god in exchange for something. Three questions in a row: where do you live, who are your people, what brought you here. Every one of them polite, well-meant, and an invitation to invent.

Plainly she was a fiend, yet the elder could not tell.

Almost the same flat sentence the narrator used of Bajie a passage ago, with two words changed: monster becomes fiend, and "he" becomes "the elder". The repetition is the point. This blindness is not Bajie's stupidity or Bajie's lust — it is travelling up the party, from disciple to master, and above the master there is nobody left to catch it. (那 is nà, 長 is zhǎng, 得 is the toneless de.)

Seeing the Tang Monk inquire into her origins, the fiend on the spot spun a false tale, and with honeyed, artful words came deceiving him: "Master, this mountain is called White Tiger Ridge, where snakes turn back and beasts take fright; and just below, to the due west, is my home.

She names the mountain, and in naming it confesses. 白虎嶺, White Tiger Ridge — where 蛇回獸怕, snakes turn back and beasts take fright. She is describing her own address as a place animals will not go, and the man she is lying to nods along. The name works twice over: in the old scheme of the four celestial emblems the White Tiger holds the west, and with it autumn, metal and killing. 起個虛情 is to get up a false story; 賺哄 (zhuàn hǒng) is to swindle and take in.

"My parents are living, devout readers of the sutras and lovers of good works, who give alms freely to monks far and near.

在堂 is the polite way of saying one's parents are still living — literally "in the hall". 看經好善, reading the sutras and loving good works, sketches exactly the sort of devout lay household that really did feed travelling monks. She is not inventing wildly. She is inventing plausibly, which is far harder and far more dangerous.

"Having no son, they prayed to the gods and made offerings, and so your handmaid was born.

奴奴 (nú nú) is a woman's self-effacing "this handmaid" — literally "slave", used the way an old letter signs off "your obedient servant". And note the detail she picks: a childless couple who prayed for a child and were given one. It costs her nothing and buys an enormous amount of sympathy. The 子 of 無子 is the noun zǐ, "a son".

"Wishing to rise by a good match, they would have married me out to another house; but fearing to be left without support in old age, they had no choice but to take in a son-in-law for me, to see them to the end of their days."

Here is the clever part. Chinese marriage normally moved the bride into her husband's household, so a married woman still living with her own parents needs explaining — and she explains it before anyone asks. The arrangement she describes is the one where the son-in-law moves in instead, usually because the wife's family has no son to support them in old age. 扳門第 is to marry upward, to climb by match; 扳 is pān, a variant of 攀, "to reach up and pull". 只得, "had no choice but", takes 得 as dé. 將 is jiāng, fronting the object, doing the same work as 把. She has patched the hole in her story in advance — and Tripitaka is about to poke at it anyway.