Shalen found it ironic that she was assigned to kill the same person who was indirectly responsible for her prosperity.
However, a job is a job. Especially when it comes to a field like hers. The most Shalen could do was try to give Eren a swift death as a show of gratitude.
Oslo was from Demonmir's faction.
He had been dispatched to get rid of Drin's party in the Badlands a few months back. But the members of the Escalon guild under his command messed things up. They failed to choose the right battlefield and allowed the White Raven's team to separate from each other and save themselves.
Oslo was called out to action by Demonmir's faction, and he agreed to it immediately. Since it was about ambushing the head of the entire party that had slipped past him, he had to clear his name by killing Eren.
