Don't beat yourself up.
She's a little kid, and little kids don't have the perspective that's necessary for them to understand why they need to do well on assessments like this one. She has no idea about school or how it works yet, so from her point of view, the test may just have been dumb or irrelevant --- even if you told her it was important.
My own DD will be 10 soon and is still struggling with the need to write stuff down and work methodically in order to avoid making trivial mistakes. It's normal, it's developmental, and she has to learn for herself. She'll be taking an assessment next week, and I'm working hard with her and trying to help her understand why she shouldn't try to do big calculations in her head. It's simply too easy to make mistakes. The message is sinking in, but she's still young and impulsive. It's normal for her age.
As for questioning her abilities, don't. From what I've seen over the years, the idea that HG+ kids sail through getting flawless results is something of a myth. IMO, having a high IQ makes you
capable of learning certain things. It doesn't mean that it's going to be
easy! Getting past impulsivity, lack of perspective and impatience comes with time. Talent is critical to success, but other factors (like the ones I noted above, for example) are important to being able to develop it. IMO, these things aren't usually innate. Plus, much of them has to come from within --- such as when a person decides she wants to achieve something and decides to do what's necessary to reach the goal. You can help your daughter and ensure that she knows she has a special ability, and your support will allow her to develop what she needs to really blossom.
As for the schools, meh. Welcome to the (unhappy) club.
So sorry to have you with us, but at least there are people here who understand.
