A loose cat in an unfamiliar house is not being difficult when she bolts from room to room. Every smell is wrong, every exit is unmapped and every person reaching for her looks like a threat, so her whole body is set on escaping any hand that reaches for her. Chasing her confirms that fear and pushes her into tighter, higher or more dangerous hiding places. The approach that works runs the other way: make the world smaller, make the room calmer and give her somewhere enclosed to run into, so that being contained becomes her own decision rather than something done to her by force.
Close Doors and Shrink the Chase to One Room
Move calmly through the house closing doors, starting with rooms well away from where she was last seen, so her territory narrows without a pursuit. Shut the front and back doors to the outside before anything else if there is any chance she could reach them, and ask helpers to guard stairways and hall junctions by standing still rather than waving her along. Check that windows in her final room are shut and that obvious hazards in it, such as an open washing machine, a recliner mechanism or cleaning chemicals on a low shelf, are closed away or removed. Once she is in one room, everyone else leaves except one or two calm people, because a crowd of anxious helpers raises the pressure she feels from every direction at once.
Slow the Room Down
Bring the lights low and keep voices quiet, low and unhurried, with no calling her name over and over and no shaking of treat packets in her face. Sit or crouch rather than standing over her, turn slightly side-on and let her watch you without feeling stared at, since a direct, fixed gaze reads as a challenge to a frightened cat. Move slowly when you must move, and pause whenever she freezes or flattens herself, giving her time to decide that you are not advancing.
Offer a Destination She Wants to Enter
Place her carrier, or a sturdy box lined and covered with a blanket, on the floor near her likely line of retreat, with the opening facing along her path rather than towards the people. Put treats just inside it, or a piece of her own bedding carrying her scent, and drape the cover so the inside looks dark and private. Then withdraw to the far side of the room and wait, because many frightened cats dive into the one dark enclosed space available once they believe nobody is about to pounce. Close the carrier door swiftly and smoothly once she is fully inside, speaking quietly as you do it, and cover the whole carrier so she can settle in darkness while you plan the next move.
Handle Only When Waiting Has Failed
Never grab at a moving cat, and never pin her by the scruff while she is thrashing, since that is how deep bites and torn skin happen for the handler and panic deepens for the cat. If she must be lifted, for example because she is wedged somewhere unsafe, drop a thick towel over her whole body, gather towel and cat together in one steady scoop and lower her straight into a carrier set on its end, closing the door before you release your hold. Once contained, leave her covered and quiet, offer water when she is breathing normally again, and let her own household know exactly where she is before anyone attempts another transfer.
One contained cat in one room is a problem solved indoors, but a cat who gets beyond the front door becomes a search in unfamiliar streets. For that turn of events, word can go out fast through KinsLe: nearby owners receive notice from the Lost Pet Alert System, and anyone finding her can reach her owner with a direct message.