Oh! Oh! Oh! I love this. Gaahhh! I won't even mention where this is taking me (as if no one will guess - but I don't want to read too much into it) but I love the sprightly, playful beginning, and then the ominous portent at the end. And the heroine knows it - but she'll go anyway. Gahhh! Incredible...
Have you ever heard the werewolf rhyme? It was supposedly handed down through Welsh folklore, but was actually penned by screenwriter Curt Siodmak for "The Wolf Man" in 1941

. Your poem would be a great companion piece!
Anyway, it goes:
Even a man who is pure in heart,
And says his prayers by night,
May become a Wolf when the wolfsbane blooms,
And the Autumn Moon is bright.
What a fine bit of verse. Yours makes me tingle even more than this one.
Damned fine, Jenn!