Because there are only three horses in camp (Khan, Chi Fu’s Piāohàn, and Shang’s horse who I will refer to as Zhuī yuè until we get a Shang and he decides the 2009 movie is not good enough for him), the captain has delegated the task of replenishing the troop’s supplies.  

Mulan and the cook or, on occasion Chi Fu himself, ride into the nearest village (an unnamed hamlet) and purchase supplies which are then toted back to Wu Zhong on a cart that (Chi Fu assured Mulan) Khan can pull alone.  Mulan did not object because, after all, Khan might not have been bred to do farm work and similar but he has done it before and anyways, how do you argue with the emperor’s consul?

This makes her slightly more mobile for the purposes of RP.

Purchasing supplies and administering first aid are the only things Mulan has succeeded at in the army, so far.  She is naturally worried that it’s not enough.