As Chief Medical Officer, Crusher was responsible for getting those injured crewman in the drive section's ward to safety. If any of those people were lost, there would be hell to pay and Crusher's head would roll. It seems reasonable to me, then, that at the time the orders to evacuate were given, and given the nature of the danger, Crusher deemed the main Sickbay wards on deck 12 relatively safe and under control and probably felt comfortable leaving it to another Doctor while she personally made sure everyone in the drive section sickbay was taken care of. Another reason that Beverly may have decided to help out down in the drive section medical ward is because they may have been shorthanded on medical staff that were needed elsewhere moving people from the stardrive section -- after all, it was a particularly busy day in the drive section on account of the entire school deciding to conduct a field trip to the drive section while the Enterprise is running with shields up, staring down the torpedo tube of a D5 Bird of Prey. I'm all for full immersion in the narrative, so I choose to believe in my own personal interpretation that the destruction of the Enterprise D is a story of bad decisions, incompetence, and laziness on the part of the crew. They're lucky that little girl only lost her stuffed animal and not her life -- among a group of kids that were seemingly abandoned in the corridor until Geordi found them, in the stardrive section during an apparent yellow alert / at least general quarters type of situation -- running with shields up into a hostile situation. All that, combined with the failure to at least try remodulating the shields, and a less than thorough examination of Geordi's visor when it was known to be tampered with, makes this operation look pretty bad. Take this and the incompetence and irresponsibility of the command crew of the Yamato, it's no wonder they stopped putting children (spoken with Ch'Pok's voice from DS9: Rules of Engagement) onboard Starships. Enterprise never even bothered to separate the ship when they flew out to Nelvana III deep into the Neutral Zone to look for a secret base. The crews of both ships should be brought up on charges, but the Yamato crew took the easy way out and got themselves dead.