One thing I have learned for sure: A person who is a good speller can "see" the word in their head as the brain transmits it from visual sight or listening. Good reading and vocabulary skills are an asset, too -- but your daughter already has those. I definitely do not associate spelling skill with giftedness.
What concerns me is that your daughter has high achievement scores, but seems to be having difficulty in the interpretation of word mechanics. With those percentiles, her overall achievement score should be at least 10 points higher. An undiagnosed learning disability could be the cause. Very bright kids can have a disability, but their other skills can "hide" the problem. I would seek out an educational evaluation for her. The testing you refer to is group-based; individual testing may give you some specific answers to her problem.