why didnt she jump?

Well she grew gradually 'stronger' and more assertive throughout the trip, to the point of wanting to drop Chris (no pun intended)

She'd found a taste for killing and he was only going to get in the way.

Because she had been beaten down and belittled by her mother but during the course of the film found herself empowered and her freedom was not jumping while his was letting go.

"All I want, is to enter my hoes justified"