First of all, there were many demons in the Forsaken Land. If she were to bring people there to build a city, those workers would become food for the demons in no time at all.
Secondly, Shen Yanxiao's target was to raise demons, not to eradicate them. Therefore, she could not bring a large team there to slaughter the demons.
The question was, how many people would be appropriate?
She did the maths. There were two groups of people that she trusted. The first group was the mixed-blood people from the Graveyard of the Sun; they were at the casino. The second group was the Cave Wolves Mercenary Group.
Shen Yanxiao was sure that those two groups of people would not make any trouble for her.
Besides, there were about a hundred people in those two groups. They would not stir any troubles in front of an army of tens of thousands of demons.