I watched this scene six times, and I can tell you that is not what happened.
To start, Carol did run into the crowd to cover T-Dog. She had a clear shot to run towards Beth and Hershel, and a clear line to run with Carl and the others. She deliberately ran after T-dog as he went to close the gate, and she went to secure their exit. She grabs the door to check for walkers inside, and T-Dog reaches the gate.
I really hate to blame poor editting, but that is really what I see. Because T-Dogg pulls the gate clased as Carol pushes the door open to look inside, and that walker is nowhere to be seen. A second later the gate is open again, and the walker managed to stumble into T-Dog and bite him. It was clear, and then it wasn't. The gate was closed, and then it wasn't. :S
But no, I don't think Carol could have done more. She was low on ammo, and the door had to be checked, that was their only way out. By the time they got to the gate, six or seven walkers were already behind them, going back just was not an option, so if there were walkers in that hall, they were dead. She didn't escape into it, she just looked in.