Little Spaniard, it's a shame you're nothing but dirt - Andalusian breed. Dirt could also ref to her color (bay).
Even if you keep moving, I'll stop you from branching out - Unicorn reference.
Not even the song of a siren could save you - Singing/healing magic.
And five is the magic number, fire and ice - Fire (Imogen uses this magic) and ice (Basin reference.