Sina yelps in wordless horror when Pel is struck, and leaps to assist her-- if it wasn't obvious before that their bonds are undone, it definitely is now.
With about two seconds to realize this, Sina pauses with the look of a startled rabbit, and then slams her hands to the earth. The brambles grow much larger and more rapidly, snaking up and around the ankles of the hunters, thorns puncturing their lower legs as they become further ensnared.
She knows she only has until the spell is interrupted, but stares at them with mixed hatred and terror as she awaits the inevitable. Eat it, harellan.