Space Pirates!
She was the one who volunteered to do it. After all, killing more enemies would yield her more loot in the end.
"I'm going to wait…"
"Wait for what?"
"To add more warriors to train," William already used more than two thirds of the warriors he levelled up already. He wanted to wait for his Heart Crystal's trees to get ripe, harvest their crystals before levelling up a grand number of his warriors.
And then he'd train these. He wouldn't hurry and rush things up. He knew he'd gain tons of ships during the war, and it was better to have ready and well trained warriors by his side to make the best use of these.
Not to mention he had to select a few capable warriors and leave them here with few ships to train other warriors on them. Once he'd gain more crystal loot, or his Crystal Heart would yield another batch of harvest, he'd come back and level up part of them.
This way he'd never run short of capable warriors. And all he needed now was to just wait.