"Pas" pour rien au monde ?

I agree with you: there's a missing pas. Pour rien au monde is just an idiomatic addition to emphasize the negation ("for nothing in the world").

Hi Adrian, l don't think 'pas' is warranted here  but l am not sure how to clearly explain why lol. I read this as, there is "nothing in the world" so, 'there is no condition (conditional) which would lead her to change her life' There is no negative meaning (which would require 'pas') on the contrary; it sounds to me like an emphasis of the negative aspect of what came before ( e.g., feedings in the night) like the ne explétif. If it is the ne explétif, l did not know that it can be constructed with the conditional. Thanks for the great question. 

The ne goes with the rien. Including pas would be a double negative: "I wouldn't change my life for nothing in the world.", which is clearly wrong.

You do find this double negative in expressions like "ce n'est pas pour rien ..." = "it's not for nothing...".

This evening, l went searching for information on double negatives in French. I learned that double or more negations are correct grammar in French, in some combinations; but not, as both Alan and Céline have stated, with 'ne ... pas' and 'rien'.  

See, 'Combining two or more negations (French negations). Fun! 

Thanks all for the explanations. These all seem like double negatives to my English ears lol.