My take on it is that she got shocked by a weird dude in the house, but rationalised, passed out and work up at noon.
From memory she heard some muffled banging, one of the girls saying 'theres someone here?' and some muffled crying noises after. Then she saw a guy with a lower face mask walk past her and go out the sliding door.
Now in hindsight and on here that seems insanely sketchy etc.
However this was a university housemate situation. People were likely coming and going all hours, half you hardly recognise.
- They had all been out separately and been drinking so she probably wasn't clear on how the night had gone, or who had come back.
- Seems like the dog didn't bark - and she probably heard two roomates getting their food not long before.
- She heard hardly any noise, most everyone would expect something like this to be a serious struggle, or at least some screaming . Who could imagine there wouldn't be, even for a drunken fight?
- She knew he was coming from the direction of rooms with girls with boyfriends. She had heard whispers concerned someone was there, then at some point what was probably muffled movements on a bed, thumping etc (which less be honest could likely have sounded like sex) then at some point, muffled cryingish noises. Then a guy causally walks past her and left.
Now all together in hindsight you go omg rapist at the least! But it's insanely rare for someone to literally sneak into a full house to rape (or murder) someone. Whether or not she knew of them repeatedly calling Maddie's ex or not, either way, this being a uni-house sneaking weird guys back for awkward hookup/cheating and some drunk crying after wouldn't be a difficult conclusion.
She probably knew it was two to a bed and figured she didn't want to deal with drunk boy drama tonight. Probably feeling it herself as well.
He casually walked out an left. Yeah he was wearing a mask, but it could easily have been a COVID mask or a scarf.
All in all I can see her making an assumption that will haunt her forever.