So far the only employees in the guild have been beast girls... we can clearly see the guild masters preference.
Also, why is she worried if they can find a more qualified person? Even if they can find a better cook who is willing to go to the wilderness, none of them can bring their kitchen with them and none of them can carry so much stufff. Frankly soeaking even without cooking as a bag carrier she more than pays her own value. Cause no matter how strong you are, you make money on loot you bring back. They can only carry so much long distance which usually means 90 percent of the stuff usually gets left behind and 10 percent of most expensive stuff get brought back. The remaining 90 percent though may still be worth half the total value.
You can also bring back cheaper materials that you would normally ignore. Just like that herb he said was low value but when you got infinite storage who cares