The reason the Anjing House did not allow Zhou Yingxue to take the mission was simple.
On one hand, it was because Zhou Yingxue was already involved in an escort mission. Although the mission target was also located in Stronghold 77, carrying out another mission would definitely affect the current one.
If Zhou Yingxue got injured or died while carrying out the new mission, that would affect the Anjing House's reputation.
On the other hand, it was because Zhou Yingxue was alone and unable to group up with teammates in the black market. At the same time, there was already a team that had set off from the black market. That group was made up of three A-rank hitmen, so the mission would be much safer being carried out by them than Zhou Yingxue.
It was not like a hitman was not allowed to take the mission alone, but since there was a more suitable team for it, the lone wolf would find it very difficult to get assigned the mission.