In what way are you certain that she's gifted?
In Seattle, there's actually a test you can take to get you into the "HCC" program which is the gifted program in Seattle Public Schools. Seattle, however, has been trying (successfully) for years to dismantle it. So even if you pass the test, there's not very many places that you can go to get these services.
Was this a test that a child could be voluntarily signed up for by their parents? In my district in a different state, the students were first selected based on standardized testing to then take the IQ test like exam to get into the program.
I'm not so certain that a test like that is proof of anything other than that someone has the resources to study for that test. Seattle's system seems to have been a magnet program (where such tests are maybe appropriate) masquerading as a gifted program. One has to wonder how many gifted students went underserved so that such a magnet program could be maintained. Sunsetting it for a neighborhood program seems fairer and more effective.
In any case, it's good that you've observed your daughter's failure to achieve without an extrinsic impetus. It's probably a good time to sit down with her and determine what excites her intellectually so that she can be empowered to pursue that subject independently. I can tell you first-hand that relying on a school or school system - even one that routinely sends graduates (minority and white, working and middle class) to highly-selective colleges and universities - to shepherd students into stable and lucrative careers is currently a fool's gambit. Academic achievement is often necessary but not sufficient (and also more expensive and time-consuming than incorporating a measure of autodidacticism.)
Most tests like this are IQ tests, and studying has little impact on IQ test scores, except perhaps showing where you over think things or take too much time. It might get you from 12% to 35%, but won’t get you from 12% to 70%.
Most IQ tests are rife with cultural biases, and can, in fact, be studied for. There's also no indication of what constitutes "passing" for Seattle's test, and how that compares to "passing" in other jurisdictions.
IMO any student that is 1-2 years ahead can be considered gifted for the purposes of parents who are thinking about how to optimize public or private education for their kids.
Based on how a lot of education systems work in the US (recognizing only discrete progress in a student), if your child is 1-2 years ahead then that's worth recognizing and start nurturing. That's about when public schools also recognize the giftedness of a student.
You don't need brilliant children to achieve this kind of advantage, just a careful eye and consistent nurturing.
The OP strongly tries to claim (before contradicting herself in the concluding pargraph) that gifted is a major psychological difference, not merely being smart and a fast learner.
Can you quote where you are seeing that I didn't get that reading at all from GP.