It has been a while since the rest of the Narnians saw what Amy and Edmund had seen while they were at the top of the How. Edmund even had to go back inside to call on his brother and inform him of the Telmarines' arrival near the How. Numbers alone, they were clearly outnumbered. Not to mention, the weapons they brought to the site that would surely put the rest of them to a disadvantage.
But this was clearly not the time for them to falter. They've made it this far. This was a war that they clearly had to win to finally free the Narnians once and for all.
After watching that display of arrival, the Narnians — with Peter's permission — decided to send out an envoy to deliver a message to King Miraz with regards to a proposed duel with the High King Peter himself. The whole time, Amy had only listened to the discussion and didn't voice out any of her thoughts about the proposal. But she knew that this was the only way they could acquire what they wanted personally. If worse comes to worst, of course, they had to prepare themselves for an all-out war.