The Song of the Sea — Was it Plagiarized?

After the sea was crossed would come
two poets worthy of this name,
first Moses, clearly hardly dumb,
then Miriam, of equal fame,
with all her maidens, singing: “I
will sing to God, for He has wrought
great wonders. Horse and rider high
above the waters both He brought
down into waters where they drown.”
Seeing how God rules the waves,
two Hebrew poets of renown
sing to the airwaves they’re not slaves,
though possibly there was one writer,
Miriam, antagonized
to Moses, siblingly indicted
for having her song plagiarized.

Exodus attributes the Song of the Sea to Moses, with Miriam’s rendition in Exod. 15:21 considered an antiphonal response. But a number of considerations support the possibility that, from a traditionally historical perspective, the poem was Miriam’s before it was Moses’.
First, whereas the poem begins in Exod. 15:1 with the first-person verb, אָשִׁירָה “I will sing,” the prose introduction says that “Moses and the Israelites,” not Moses alone, sang the song. Moreover, it refers to הַשִּׁירָה הַזֹּאת “this song”—not “his song” or “Moses’ song.” Thus, the biblical text itself is not so clear about attribution. This is the reason why in the last verse of his poem I suggest that Miriam’s  complaint about Moses in Num. 12:4 was motivated by her belief that his ascription to himself of the Song of the Sea implied he was a plagiarist, an opinion that the Book of Numbers implies was rejected by God when He inflicted her with an obscure  dermatological disease, that probably should not be identified as leprosy.