Partial, possible solution... (or at least theory...)
From hint #1:
arMy is an anagram of Mary
From hint #2:
the (word number 2), little (3), had (7), and a (8) are going to be difficult to anagram, so not all words are...
From hint #3:
Sherry, my nurse => Nurse Sherry => Nursery (rhyme)
Given these, it seems we're dealing with:
A jumbled, cryptically described, homophoned, and partially anagrammed nursery rhyme, possibly Mary Had a Little Lamb(?).
In detail, we have:
Wow, the little negative cow army had a balmy sun war.
army had a => Mary had a
little => little
balmy => lamb(y)
sun war => run was => flee was => fleece was
...white as snow?
(unused bits: Wow, the negative cow)
Not really sure where to go from there. I'm obviously still missing something, but thought this might at least be a starting place for someone else...