Heart of Dakota teaches skills in a very purposeful, incremental manner. Spelling is taught in the younger years via spelling lists that utilize pre-dictation type skills. After that, dictation levels 2 through 8 are used to systematically teach spelling. Dc move incrementally through these levels at a pace that fits their abilities and skill level. The WG guide has several dictation levels in its Appendix. I would start your dd with the easiest level and see how she does. There are excellent directions for the proper steps to do dictation at the start of the passages. Following these directions consistently and carefully helped our ds who was previously not a good speller become an excellent speller. This took time and patience, but it worked.

I'd suggest doing dictation daily instead of only when it is scheduled in the plans. We did this with our ds who needed to improve his spelling, and it only added 10 minutes to do the day. Well worth it - time well spent.
Heart of Dakota also provides ample help with 'editing' work. By consistently following the editing checklist in the Appendix of the guide, our dc have learned and are learning to proofread their work more carefully. I make it a rule to correct work as soon as possible, and always within the day, to help fix bad habits and instill good habits.

So, all work must be edited and fixed right away using the methods described in the Appendix. This has helped our dc pay attention not only to proper spelling within their writing, but also to proper mechanics and usage within their own writing. The Essentials in Writing composition plans also encourage editing with rubrics and checklists, and by following those guidelines, our son's writing has improved overall each year of high school.
Finally, Heart of Dakota uses an outstanding English program. It teaches English in an incredibly thorough way that carries over to students' own writing. They can hear and see 'what looks right' naturally from having worked through R & S English's lessons. R & S English is not just a grammar program, it is also a writing program of sorts as it teaches grammar for the purpose of good writing. I was amazed at how easy it was for even my 8 yo ds to take his standardized testing on 'word usage, capitalization, and punctuation' this week. He could just hear and see 'what looked right' thanks to both dictation and R & S English.
So, you don't have to add anything to the HOD plans - hooray! All you need to do for your dd to improve her spelling is to consistently follow the WG plans for LA in all areas (daily dictation passages, scheduled written narrations, scheduled Essentials in Writing assignments, and scheduled R & S English assignments), while also making sure to edit carefully and consistently in all subject areas. You will be shocked at how much this improves dc's writing over time! It is effective because it is all directed at improving student's personal writing, rather than just completing worksheet after worksheet of correcting someone else's mistakes in writing or spelling. I just want to encourage you to trust HOD's plans! The results are amazing. HTH!
In Christ,
Julie