Corrected entry: The reason for sacrificing Rosie (not sending a rescue party out for her), following her crash, is given by Hunter, when he says "We are running on fumes", suggesting that they urgently need to land, and the Rapiers are seen flying back and forth in the equivalent of a holding pattern, but since it was established earlier in the film that the Rapiers can totally shut down and power down their engines, they could have powered down, conserving fuel, and given the rescuers time to save Rosie. It's not like they need their engines to maintain lift, as do conventional aircraft, they are in space.
Corrected entry: Following Rosie's crash into the flight deck (after her collision with a Kilrathi fighter), a remote operated bulldozer is sent out to push her fighter off the flight deck, when it does, her fighter falls straight down off the deck, as it would on a planet with gravity, but it is space so it should have just floated away.
Correction: It is more than likely that the technology used to create artificial gravity on the ship encompasses an area that goes beyond the hull (as evident when the Rapiers launch and also when firing missiles). Everything starts going straight "down" once off the stability of the deck or tube. Rapiers also need to launch quickly in order to get outside that gravity field.
Correction: The actual reason is given by the launch commander, that they need to get out of there since there is an approaching Kilrathi fleet. The use of the expression "We are running on fumes" is simply to urge Angel into making a decision about Rosie's crashed Rapier. Also, assuming the Tiger Claw has a gravity field encompassing an area beyond the hull, they would need the landing strip cleared so that the Rapiers can land as traditional ships would on an aircraft carrier since once they are within the field they would have to obey the laws of gravity.