Because Eponine's body was slowly losing the ability to feel due to her wish, and cold already had a numbing effect, cold became one of the first sensations she stopped being able to notice easily.  So the cold wasn't bothering her as Violetta expected though, it did make her muscle movements alternate between sluggish and erratic at times, the effects of slowed muscle metabolism combined with the instinct to shiver.  This didn't make it any easier for her to traverse the ice trees as she followed Violetta, lagging a bit behind.

When they saw the giant ball of ice hovering below them, Eponine was bit relieved.  It was large enough that she could land on it without slipping and falling into the endless sky, and it seemed like the likeliest place for the witch to be.  Without another word, Eponine jumped down from the branch she was one and right before she hit the ice ball, turned on her shield and activated 'reject', making sure that she incurred none of the damage from the fall while transferring all the force of the impact into the ball.  What happened next would depend entirely on how strong the ball was; would it absorb the shock, would it shatter, or would it do something else entirely?