I feel that as she becomes more malleable to accepting new situations - and especially as she starts to seek for them - that can lead to more exploration beyond the norm.
For example, D is already coveting voyeuristic, incestuous, group and shared partner (with interracial!) experiences - I see bestiality as a big step, but still just another new thing to wonder about . . . especially since we're watching her become so easily influenced by new ideas that come before her. Look at what a simple porno movie night did to get her open to new experiences, for example. Since legality/morality is more flexible in her universe, I see that act as one of a single moment that just happens with the right circumstances, probably enabled mostly by the real kink-meisters in her life such as Elena.
Honestly, with the trajectory this game is going, I would really be interested in a WTF?! moment the morning after for these characters, after all the steamy stuff is in fully open mode. Bestiality could be that event which slaps them all a bit and makes them wonder where everything is going and if something needs adjustment.
This game has gone to various places, figuratively speaking. What's one more type of experiment to try? And make it optional, certainly.
