Thank you so much for your responses. It's good to know I'm not alone. Both my sisters have kids, and neither my nephews nor my nieces exhibit any sorts of the behavior issues DD has. They just don't understand what I deal with on a daily basis. I guess it is a good thing she vocalizes and externalizes her feelings as I struggled a lot with internalizing things growing up. I've had issues with depression and anxiety my whole life and worry that I've parented her wrong, but on the other hand, I would have never had a meltdown in front of schoolteachers or classmates as a child. The teachers have mentioned perhaps getting her into cognitive behavioral therapy to help her cope with these issues.
For a long while, I actually debated whether DD could even cope with public school or if we would have to homeschool her, but I felt like she needed the socialization (especially being an only child). In kindergarten, she wouldn't even play with other kids, but by first grade, she made 2 good friends, so at least, she will play with other kids at recess.
But her behavior problems...ugh! I know she doesn't have ADD or anything because she can concentrate absolutely on books, schoolwork, etc.; however, she gets so excited and hyperactive when she knows the answer to a question the teachers ask the class (which is nearly always), she must get out of her seat and run all over the room with her arm raised. I imagine it must be exhausting to be her teachers! I'll be sure to get them a great end-of-the year gift as they have been amazing.
The funny thing too is that despite all these meltdowns, DD loves school and dislikes it when there are school holidays.