Haven't read the novel, but that was pretty obvious. First off, she's far too young for this relatively "realistic" fantasy world without any 16 year old godlike heroes running about, and then she was too childish and too low on stamina to be among the best the adventurer guild has to offer, even if you consider that Lecan is in his own class, if the merchant expected them to keep up with a horse for a whole day, it's obviously something normal for this world's adventurers.