Why Helena could not safely remain with Juneau

What could Helena have done for Juneau during the withdrawal from Guadalcanal in November 1942?

With the available escorts already protecting damaged ships, remaining behind could have endangered the whole group; only an additional destroyer would have made a rescue attempt more practical.

The formation contained damaged ships and too few sound escorts, leaving no safe option. The surviving undamaged cruiser and destroyer were already needed to protect vessels that could not withdraw safely alone. A spare gun-armed destroyer might have remained to rescue Juneau's survivors while still escaping before daylight. Detaching one of the escorts actually available, however, could have exposed the whole damaged group and cost more ships and lives.