She could be smelling the Gerbil or she could just hunting because it's night. All our snakes cruse at night and 'hunt', especially if its close to feeding day. I wouldn't worry about keeping the Gerbil in the same room. Just be aware when she's in feeding mode and leave her be as with any snake in feeding mode. We've raise ASFs in our snake room for a few years and it never created a problem. It was actually helpful when we had an escape last year, the escapee was found under the ASF shelving unit,.