It's all AU.

"...ok that's not right." Kaylee blinked, looking back at the innocent brown door she apparently just walked through. The innocent brown door that apparently belonged to the small cafe she'd just walked into.

It was a lovely cafe, really, very pleasant. The only issue she took with it was that it wasn't the engine room.
That isn't to say that she took issue with every room that wasn't her comfortable, familiar engine room back on Serenity, but when one attempted to walk into said comfortable, familiar engine room and ended up in an entirely new place that didn't look like anywhere she recognised in the 'verse, well, it was enough to put anyone off.

"What's going on?" she asked out loud to herself, confused, for the moment, even out of her usual sunny smile.