Mountain Eagle sent Marta away because she was clearly not fit for the interrogation situation. There are some things that are hard to explain to an underage girl in just a few words; it's better to let her experience them on her own...
The two Indians who were in contact with spy Martha were clearly mercenaries...
Mountain Eagle was unsure of their exact numbers, but one thing he was clear about was that, according to what Killing Bee had previously mentioned, the Anglo-American Intelligence Organization had employed more than one team of mercenaries.
These people were now lurking around Kamui, so it was absolutely necessary to inform those tourist reception venues to try to squeeze these people's room for movement.
There was another point that Mountain Eagle reckoned even if he told Marta, she would probably not understand...
Mountain Eagle took over the mission from Chief, and taking over meant he possessed a certain degree of power!
