The Eighteen76 Balcony and Chase Bridge seats offer significantly different experiences - especially for a concert. The biggest difference between the seats will be distance to the stage. The balcony sections are the farthest seats from the stage so for a high-energy concert like Twenty One Pilots, being so far away may leave you a little dis-engaged. The Chase Bridges, on the other hand, are suspended over the 200 level and come with a certain wow-factor just from their setup. They're also much closer to the stage, although they will be very high up.
Barstool seats are very common among the younger drinking-age crowd because they're easily to socialize from, and are also very accessible to drinks and concessions. They would be fine for a 12-year-old, though she likely would not "appreciate" them as much as someone a little bit older.