SPOILER Why didn't the vampire Victoria do this when she had the prime opportunity?

In the movie New Moon (don’t judge me I was just poking around), Bella jumps off a cliff and the wave overcomes her, when she is in the water she sees Victoria swimming towards her but is then knocked out and Victoria just ignores her and swims the other way. After she is saved by her oh-so-terrible-acting-knight-in-tanning-armor Jacob Black, you see Victoria watching from afar in the water. Why not just kill Bella when she was so vulnerable?