According to the dictionary, "to spoil" means "to destroy/ruin" or "to treat well".
So what does "spoiling" mean in the sentence of "she is not spoiling for a fight"? (as in "she is baited to have a fight, but she is not spoiling for it".)
I interpreted it to mean "to treat well". But if so, I would have written it as "she is not spoiled for a fight". Or did the author use it in the context of "to destroy"?