Amelia needs to not be willing in order to escape a Consensual Predator. The dialogue usually hints at this, but if the red button says 'Pretend Struggle' instead of 'Struggle' then Amelia is indeed willing. If you hit 'Cramped' until Mood goes below 7 or Drive goes below 5 Amelia will become unwilling and then you can either get out through Escape or doing enough damage with Struggle.
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I suppose my last comment is slightly inaccurate upon thinking about it. The reason you can escape Bunny girl while willing is because a behavior I'm aiming for with her is that she is doing it for fun. So if Amelia 'Ask for Freedom' or does 'Escape' after a certain amount of time as prey, the Bunny girl will ask and cooperate in getting Amelia out if interested.
Neko, meanwhile, is playing for keeps, so 'Ask for Freedom' and 'Escape' do not cause her to ask if Amelia wants out at any time. Since she's only the second Consensual Predator to get added I can see how this flip in behavior can be jarring, but hopefully the mechanics of the game make more sense as more predators get added.
The two available Consensual Predators are on opposite sides of the spectrum. Future Consensual Predators will likely fit in somewhere in the middle where there'll likely be another way to escape while Amelia is still willing, though not as numerous as Bunny girl.
For every Consensual Predator: escape is possible while Amelia is unwilling through either Struggle damage or passing Escape enough times.
Besides that: Depends on the specific Consensual Predator. Less serious predators will offer to let Amelia out (Bunny girl) while more serious ones are less likely or won't at all (Neko girl)