My Dd at 4.10 had an IQ test that seemed low to us. She did not have anxiety, but she definitely did not have good rapport with the tester. In fact, I had rarely seen her engage in a will power struggle as the one she had with the tester while tester was building rapport (did not happen!). We retested a couple of years later and the results were completely different, higher than what we had suspected.
I guess for your Dd, it could happen if she had felt anxious that day in particular or about the testing experience.