Could NASA have sent another shuttle to rescue Columbia's five men and two women?In theory, yes.
Normally, it takes four months to prepare a shuttle for launch. But in a crisis, shuttle managers say they might be able to put together a launch in less than a week if all testing were thrown out the window and a shuttle were already on the pad.
Columbia had enough fuel and supplies to remain in orbit until Wednesday, and the astronauts could have scrimped to stay up another few days beyond that. With shuttle Atlantis ready to be moved to its pad, it theoretically could have been rushed into service, and Columbia's astronauts could have climbed aboard in a series of spacewalks. If Atlantis flew with the minimum crew of two, it could have accommodated seven more astronauts.
Not suggested here, but also possible is a Russian Soyuz rescue, or even resupply, prior to a shuttle rescue. The Russians just yesterday (IIRC) launched a resupply to the ISS.