This is why Soverick said their motives were complicated. They came to capture her, but they also planned to eat her. Either way, they couldn't go all out, or they would kill her by accident, or she would escape in fear.
To eat her, they had to let her body grow so that they would have more food to eat. But if they did that, she would become very strong. If she becomes too strong, then they won't be able to hold back in trying to capture her, and she might escape if they display too much of their power.
Finally, they had to corner her and leave her with no other options so that they could capture her. They had to do all of these while adhering to the information she had about them from the Stellaris plane and her estimation of what a new Origin god could do.
