The vehicle ramp that Steve uses to stop the merc's car is obviously just lightweight sheet-metal, since it sags and flexes and bounces and rattles freely as Steve moves it around.
The Countess witnesses Steve lift the car of her abductor off the ground while holding up a metal ramp, then throw the abductor through the air with one hand. Yet she doesn't Seem to find any of this unusual.
When the Countess leans over to climb down through the opening in the museum's ceiling, her head protrudes sideways well past the edge of the door to the serviceman's cabinet, and so the watchful guard would surely have seen her.