Who is to say Alison wasn't drugged and that she normally wouldn't participate in such sex? That Jeremy isn't "corrupting her" behind the scenes? There's more than one time where Ian notes that Alison acts surprisingly uninhibited and in a manner he'd never think her to act. And she also keeps escalating her wild behavior.
(this is of course just playing devil's advocate, but the point is, we have zero information in both cases. But in one we choose to jump to conclusions, and in other it doesn't even occur to make such conclusions to some people. One could very well say that's just more of those supposed double standards)
Right, precisely: it's ambiguous, if you want to be nice about it. Or a pure conjecture in terms of what we know, if one wants to be blunt.
Claiming that Holly got raped and that Ivy is a rapist "but she gets a pass" as if this is some sort of established fact instead of nothing but a wild fan theory, that's presumptuous, as best. It goes quite beyond calling it out as a potential rape.
edit: Also, it may be worth to remember this game doesn't have rape
tag. I really doubt EK is developing a "Ivy is raping Holly" storyline here.