Although she hadn't mentioned it to Grandpa, the Hero wasn't very skilled at dealing with Chocobos before acquiring the Phoenix Bloodline.
1. Hadn't ridden one before
2. Not adept with Chocobos♛
D2=d2(2)=2
It's hard to say whether it was because snakes are part of their diet, or because the high-tier Chocobos used in her initial training were too proud and not very approachable.
Just as she didn't know why she was so good at calligraphy, she wasn't consciously aware of her unfamiliarity with Chocobos.
Perhaps people have their own individual personalities just like that.
The two Chocobo companions of the coachman had been quite friendly toward her even before she gained the Phoenix Power; they must have been especially docile by Chocobo standards.
Though she ultimately learned basic riding skills, unlike her calligraphy, it was limited to just that—she could stay on the bird without falling off.
