Video footage of Viola's Gym Battle:
Be warned, major spoilers so don't watch if you're the kind who wants to do a blind playthrough when you get the games. Now some interesting stuff I uncovered thanks to this, Viola's Surskit knows Bubble and Water Sport so that can really be a surprise if you chose Fennekin and were expecting yourself to have the advantage because not only can it hit you super-effectively, but also nerf your Fire attacks. Also, those who chose Chespin will have their beloved Grass chestnut struggle against Vivillon due to it being 4x Grass resistant and having attacks hitting Chespin super-effectively. Froakie also faces the problem of its Water attacks being resisted by Surskit so I have to say Game Freak really did a good job here to ensure no starter has the advantage.
Thankfully, based on this and other videos seen in this thread you can get Flying-types like Pidgey early, and heck even Pikachu would do great against her Pokemon due to them being Electric-weak. Basically, if you don't have Pikachu or a Flying-type you may have some issues. Going by the player's team, it seems you can get Farfetch'd early as well if I recall.
Player's team in the video: Froakie, Pikachu, Fletchling, Burmy and Farfetch'd.