Etymologically Correct Character For The Sichuanese ‘niang’ Meaning "What"
There is a better link to the article that is quoted above in this post on Sina Blog, which will let you search the whole article in your browser. 

The article mentions the use of 合音字 in Qionglai and related Sichuan dialects, i.e. one character writing two syllables. Examples the author gives include “不晓” 写作 “表”，and “那样” 写作 “浪”.  Possibly 娘 is simply a 合音字 for the interrogative form 哪样.