So they sneaking out of the water or the ground or some window ledge or just under her bed and grab Anne's legs or feet to pull her in, she trips and the direction you choose her to fall decides if she is Anal Vore (Pred) scene or Oral Vore (Prey) scene?
I was thinking something a bit different. Take the shark girl for example. In this case, Anne would be walking on water and maybe as she finally hits land and achieves, the shark girl jumps at her and falls face first into Anne's butt. Meaning that this would be an ending to the predator no matter what. It's just that just like the shark girl, if she got caught in the water, she would lose. Once she's done she "wins".
But I do like your idea as well. That could definitely work with some ghost girl grabbing her legs and if she falls on top of the ghost she AVs it but if she falls in front she gets eaten.