If she’s driving that thing down Main Street, it’s hardly a secret.
There’s much that’s wrong with this: it’s not a carpet, for one thing. It’s a bedspring. There doesn’t seem to be any reason it’s attached to the motor; it adds no aerodynamic properties - a fact emphasized by its steep, perilous trajectory into the streets. (Speaking of which: Smallville got real of a sudden; turned into a crudely colored 50s postcard.)
Finally: if Superboy had a sister, then Superman had a sister. If this was really the case, it would have come up in a movie or two now and then, no? Here's the description:
When little Kathy Warren (who is staying with the Kents until her mother, Martha Kent’s friend, recovers from an auto accident) accidentally bursts a space-brain that Superboy has captured, her intellect is raised to genius status.
All from busting a space-brain. A pack of nonsense, as usual.