That’s really sad.
I think this is going to be a problem that keeps getting bigger and bigger, particularly in poetry, which is in some sense about concise and sparse language.
We are at the point where most poetry ever written is accessible with a wave of the Google; but more, with God knows how many millions of poems out there, what are the chances that you were the first to utter the felicitous turn of phrase you think you invented?
More, when you have read thousands of poems, how can you find your own voice?
Not that plagiarism isn’t still possible. Copying a piece wholesale, or imitating it line by line as in the examples you gave, is still obvious plagiarism.
But what about poems that are obviously “original” and yet derivative, clichéd or hackneyed?
I used to work with a musician in a band who had written a lot of excellent, original pieces — but as his inspiration started to run out, he started creating near-clones of famous pieces. Oh, not plagiarism — the rules in music are very clear and he was always clearly further away than the rules suggested. But still, in almost each case I could identify the specific piece that was being used.
There was a low point when a production of his, one which I was in, got written up by the Village Voice, which identified the source of a specific piece.
We’d argued about that piece. I said it was far too close to a lesser-known piece on a very famous album by a very famous band. He said, “No one will know.” And here was the Voice, naming it specifically in the first paragraph of their review.
What to do when the well runs dry? I don’t know. My once-collaborator was in his rights to do a “sound-similar”, and yet it justifiably resulted in a bad review. Your ex-friend just up and cheated; that’s never acceptable.
Finally — I personally, random internet person whom you will never meet, give you absolution for having reported your friend. You did exactly the right things, except for the freaking out part ;-) — and that was basically an internal monologue of yours, so only we know.
She was diminishing everyone else’s work this way; it had to be stopped. She should have got the message when you approached her — she should have spoken honeyed words to you, at least cut back on the obvious lifts or giving attribution. She forced you to the point where you had to pull the fire alarm. No blame accrues to you except for you making yourself miserable as a result, and there, you have no one to yell at but you. ;-)