Journey to the West: "Mother of wood"
comparing the original text, with the english version you provided; i would say, most meanings, details and metaphors are lost.
the scenario that &quot;mother of wood&quot; was caught, and recused by &quot;mind ape&quot; is paragraphs 9 - 11 https://ctext.org/xiyouji/ch63/zh
rant about the translation:

When the mother of wood was taken by the water monster

the monster is a (nine-heads reptile &quot;九頭蟲&quot;)

One used his secret skills to open the locks

well, the &quot;mother of wood&quot; was tied on the pillar (那獃子綁在柱上). later, mind-ape cut the rope by bite (行者四顧無人，將拑咬斷索子叫走). no locks lah.
such translation, is like, &quot;middlemarch&quot;, or &quot;pride and prejudice&quot; in 500 words.

what is mother of wood meaning? yellow-wife?

first of all, the book &quot;journey to the west&quot; is full of taoism metaphors.
then, there're two main groups of taoism, alchemist (外丹) and internal alchemy (內丹). further, over thousands of years, there're many sects, which explain taoism literatures in completely difference ways.
yellow-wife should be &quot;黃婆&quot;, a more precise term should be yellow matchmaker (黃 + 媒婆). the metaphor is:
a matchmaker let males and females to get married, intercoursed, producing offsprings. he/she should never be part of the &quot;children production&quot;.
yellow matchmaker (黃婆) means the element earth (土), which has the colour yellow.
in 悟真篇闡幽, stated

眞土又名黃婆
調水火而和金木者也

the original text is longer, with more metaphors. here's a brief explanation for beginner.
the yellow matchmaker (黃婆) is to mediate between other four elements: water, fire, metal and wood; it do nothing by itself.
back to the journey to the west, the third disciple (沙僧) always was the mediator between the first and second disciple. that's why the author assigned the nickname yellow matchmaker (黃婆) to him.

what is mother of wood meaning? yellow-wife?

mother of wood is 木母, this nickname is assigned to the second disciple (豬八戒). i can't get the rationale at this moment.
frankly, if you have knowledge of taoism, this book is more funny :)