Sorry, your poem needs a rewrite.
I'd love to see more poetry about the 'dirty, nasty, filthy affair of [Joseph] and Fanny Alger's'! Please contribute!
She didn't help, she was a victim.
Indeed, some interpret her as a victim (and I'd probably count myself in that category). At the risk of some kind of hermeneutical faux pas, I'm not sure anyone would seriously consider her a co-author to Joseph's development of the early LDS marriage dynamic; rather, the 'affair' is often interpreted as a pivotal moment for Joseph's arriving at the inspiration, post-hoc as it were, as a means of conveniently explaining the affair and its justification, as well as opening a codified justification for a secretly-guarded doctrine of plural marriage among early LDS leadership.
'A little Fanny' intends an interpretation synonymous with 'the affair' as it were, and 'helps' intends an underlying sentiment of inspiration and pressing urgency in the matter of Joseph's salvation later in the line—we, the readers, participate in Joseph's urgency to compose a coherent narrative of explication for having found himself there in that barn under circumstances unbecoming of his allegedly profound role as the interpreter of God and Creation.
An American Victorianism would've indicted Joseph, and we've every reason to expect the obviousness of his sexual promiscuity to destroy all confidence in his prophetic ability, as is so powerfully conveyed in line 3.
In a sense, the reader gets to participate in accusing Joseph, and the weight—the sheer damnation levied against Joseph's character in the words 'an affair'—almost certainly spell the end of this chapter for Joseph, for Mormonism, for this response in antebellum America to capitalize on do-it-yourself exaltation.
But no, even with this obviousness, we have line 4; a reflection of line 2 and an appeal to our word 'helps'. 'He', Joseph, the so-called prophet, by now alone and abandoned in a now-metaphorical conception of the barn which gave rise to the would-be pit of Joseph's ashes! He alone, relying on his prophetic talents attributed to the divine, found within himself a narrative for redemption! 'Found'!! 'Revelation'!! 'There'!! Joseph's transformed his hell-in-a-barn for celestial glory and a legacy among his followers that echoes into the present.
It's on the credulity of Joseph's ability to reveal that he finds redemption among his people, and we're back at line 1. 'A little Fanny', a footnote and a beginning, but ultimately disenfranchised of an identity in published Mormonism; her memory diminished and her narrative reclaimed by the credulous.
The end of line 4 and the end of line 1—'there', 'the barn'—really became two places for two people with two different destinies. That barn belongs just as much to Fanny as it does to Joseph, and it's Joseph's revelation that pretends to lock its doors and keep her there as a purportedly willing and obedient participant, unable to escape its tragedy.