>>709
Yes. 「ないのです」 almost always turns into 「ないんです」 in daily
conversation because it's easier to pronounce.

> Is it to connect "ぬる" with "娘"?

Sort of. But I think it's different from the 「ん」 of 「ないんです」.
The author may have had the word「どろんこ」(= kids word of mud) in mind.
I'm not sure.