Why doesn't Lyra Obey Lorek's request to wait for him once she is across the bridge?

The bridge collapsed behind Lyra.... she couldn't return and Lorek couldn't follow.

The bridge held. She took another step, then another, and then she felt something settling down below her feet and leaped for the far side with all her strength. She landed belly-down in the snow as the entire length of the bridge fell into the crevasse with a soft whoosh behind her.

Pantalaimon's claws were in her furs, holding tight.

After a minute she opened her eyes and crawled up away from the edge. There was no way back. She stood and raised her hand to the watching bear. lorek Byrnison stood on his hind legs to acknowledge her, and then turned and made off down the mountain in a swift run to help his subjects in the battle with Mrs. Coulter and the soldiers from the zeppelin.