Sheridan would consider herself fairly well acquainted with the house she's in. If it had secret passages or the like she'd not found, this wouldn't particularly surprise her, but not needing to risk a beating to walk around means a few days is more than sufficient to establish knowledge of the overt areas.

It does not, of course, require being acquainted with a house to know that purple-blue-black apparently-not-especially-amenable-to-vision whirlpool-like things are not generally present above the kitchen table. 

This one is there when she turns around. It proceeds to swallow her.

The place she sees around her when she is no longer swallowed is not one she is acquainted with in the least.