Hi darling!
She found herself on a far western shore,
with the ocean before her;
like a giant that pretends to slumber,
until it wishes to ravish the town.
So I forget exactly what this error is called, but you've executed it rather hilariously. Due to word order, you have me thinking that she is "like a giant that pretend to slumber, until it wishes to ravish the town." Now, I know you mean the ocean, but because the her is next to the parenthetical expression, it's syntactically logical that the expression is in relation to her. Since you're not, I think, trying to rhyme between her/slumber, why not:
"She found herself on a far western shore,
before her the ocean lied
like a giant pretending to slumber
until..."
Removes the error altogether and reads a bit better, but try going for your own version of it.
There was no Jack in sight,
she would tumble down on her own,
down the beach and into the water.
My biggest problem with this bit is that the punctuation is not properly reflected by the phrases. The first is a sentence, the second is a sentence, so something different needs to happen there other than a comma. Also the repetition of "down" isn't too great.
Ashes, ashes, we all fall down.
I find this rather out of place. Since I know the history of the line, and that the poem is about suicide and not about the black plague, it doesn't seem to fit at all. It's not witty or anything and I think you'd do better to create your own wonderful line that actually works instead of using someone else's
Now to look at the poem as a whole. So from the title I can tell you're trying to do a mother goose - grim fairy tale kind of thing. As far as Brothers Grimm go, the only bit you've taken from it is suicide, when the stories themselves are about much more than just grim things. Mother Goose-wise, the only things I can pick up on would be "jack and jill". So, in general, the title isn't very accurately reflected in the poem. The poem itself could be witty and cute and morbid but it's just not there yet. It's about suicide - and yet I feel
nothing when I read it. You're just stating facts instead of creating emotions and feelings. It's very to-the-point, which poetry can be, but it has no effect. It needs some kind of oomph, and right now I don't feel like it has that. How you choose to do that is up to you. Imagery, symbolism, metaphor - whatever.
I hope this helped and I didn't give it too much of a beating. I tried to be specific but not over the top. It wasn't bad by any means, but the oomph is important.
"I also remember Suzanne broke the world record for longest critique, quoting every word I used individually and discussing it for paragraphs. She concluded that I was a better poet at 16." - Firestarter, talking about his Reviewing Sunday dream.