It sounds to me like there are both initiation and sequencing issues, which are more in the category of executive functioning/planning/organization problems. If she's having difficulty prioritizing thoughts to put in writing, that's an EF issue, too. When you are scaffolding her writing at home, you are being her frontal lobe. I would agree that having an SLP look at her would be good, and maybe a neuropsych, too, for the EF questions.
Multiple spellings is highly unusual in children this age and of this ability, and is a significant clinical finding. Might want to tease out whether that is an EF issue (poor self-monitoring, so that she might actually know the same spelling for a word (correct or incorrect), but doesn't have good "quality control" for what she actually puts down on paper), or poor phonological processing, and hence lack of solid orthographic mapping of sound to phoneme.
I think I have mentioned elsewhere that older and cognitively high functioning kids with underlying phonological processing deficits often do well on the simpler phonological processing tests, and need careful attention to phoneme manipulation (e.g., deletion, reversal) tasks, especially those using nonsense words.
