Our gym has been doing some intensive vault training recently since we were getting killed in the all-around on that event! I know when my arms are bent and I don't get repulsion, it's because I'm not standing up on the board. It seem counter-intuitive, but she should feel almost like she's leaning backwards a little (stay tight!) when she hits the board. A good drill one of my coaches, who's a very good spotter, does is that she stands between the table and the springboard while the girls vault. She helps to lift you up and over her, but the girls also go higher automatically because they really don't want to hit her.
Once she's getting a better pop, we work on hollowing off. We stack mats behind the table and land in a hollow position, and then put a wedge mat, big side away from horse, onto those mats and the key is "don't let your feet touch the mat", and land in a hollow. The first time we did this we had a spot to keep us from sliding back down towards the vault table.
