It is hard to say without observing your DD directly or having an idea of her level of ability as regards perceptual reasoning, verbal reasoning or visual spatial skills. Having exceptionally high working memory or processing speed wouldn't prevent the types of difficulties you described. Actually, if this weren't a gifted forum, I would automatically say that the difficulties you described are mostly age-appropriate and developmental. In general, understanding over-arching concepts extremely well is a long ways from mastery of those concepts and the ability to consistently and correctly apply same.
Assuming that her relevant abilities (PR, VR, VS) are very high, frequent occurrences of transposing numbers, improperly lining up numbers, and misreading/omitting keys words may be signs of mild issues related to dyslexia/dysgraphia if other signs are present. In the absence of other unusual circumstances, the other four types of mistakes suggest a lack of developmental readiness to me. I have no professional training so take my post with a grain of salt; incidentally, those were the types of abilities on which our district GT office tested DS at age 7 to conclude that he can be SSA into a compacted 3rd/4th math class. For example, your missing addend problem is elementary algebra, which they try to introduce in mid-elementary to enrich and stretch students. Number value was one of the key ways teachers assess mathematical understanding. Similarly, the ability to translate multi-step word problems into the correct mathematical equations evidences mastery of concepts as well.
If she is very gifted in PR, VC, and VS, then I am more inclined to think that your DD may have been deprived of strong teaching in math and she is one of the kids for whom strong teaching is critical.
