I can see D getting entangled with a doggie by its curious, unintentional involvement and her just going with the flow after a certain point. Perhaps she's already in the middle of some activities and Bubsy surreptitiously butts in at an opportune time (from his perspective), but by this point she's already so deeply comfortable with her sexuality and involved in an activity that she only lightly recoils and otherwise rolls with it for that time. Therefore, it becomes a one-off, maybe with some surprised/shocked encouragement from those (humans) with whom she's mingling at the time. If Elena wasn't somehow involved in helping such a scene continue, I'd be surprised. It becomes something upon which to look back on and smirk or sigh, because who would look at that woman in later years and suspect she had that ONE TIME WITH A DOG, etc.
That is, I feel D being sweet doesn't mean she can't be kinky and "flexible," even to short-term extremes. Plus, as the floodgates are opened, her focus on the limits of what to experience could be blurry for a time, especially if the MC isn't there to help be her rudder as she moves ahead. As others have mentioned, she seems to have a submissive streak in her which might help move such a scenario along. It might come off as a weird, yet otherwise curious kink she allows happen, but could lead to her support network rethinking just how far she's "out there" at the time, should this occur at a point in her arc where she's possibly losing her sense of self at all (i.e., sensory overload leading her ability to process it all).
Musing ... at least for people I've known directly or through others (and, I'm kinda old), lots of otherwise average folk have moments in their backgrounds - sexual or otherwise - which general society would otherwise label as abhorrent or deviant. Skeletons in closets, youthful escapades ... labels are in the eye of the beholder. I was a very straight shooter who - for a time - was a too-clever prankster, if you ask my then-childhood friends; I was a callous and costly destroyer of private property, if you ask my then-childhood neighbors. Regardless, such events need not define or deeply taint such people in the long term, but could instead be understood as point-in-time happenings which brewed from prior contexts that may no longer apply ... and from which their views of themselves and the world are still at least partially informed.
