You are making a wise move in seeking another approach for teaching your daughter to read, write, and spell.
Your choice of The Spalding Method is excellent as the method derives from the work of Dr. Samuel Orton, a pioneer in working with children who had disorders similar to what you describe.
The Spalding Method as outlined in The Writing Road to Reading is a systematic, multisensory approach to learning language. Students learn 70 common phonograms which represent the 45 spoken sounds of the English language. A phonogram is a single letter of fixed combination of letters each representing one sound in a word.
Children learn to form the letters of the alphabet accurately and precisely by following specific directions given in the text. The combination of learning the sounds of the phonograms along with the writing of the phonograms is the foundation for decoding and encoding words. After approximately 45 phonograms are learned, students begin writing words in a spelling/vocabulary notebook by saying the sounds in each word and writing the phonograms which represent those sounds. Words written in the notebook are taken from the Extended Ayre List also found in the text.
After approximately 115 words are written in the notebook, students have a bank of "frequently used words" large enough to begin writing original sentences. After approximately 200 words are in the notebook, they have a large enough bank of words to read simple, decodable books.
I encourage you to begin this program immediately with your daughter and to continue it intensely through the summer months so your daughter can enter second grade feeling and being competent in reading, writing, and spelling.
No particular modifications are needed other than to keep in mind that it may require a larger number of practices to learn the phonograms, and it may require more time spent in practicing. You will need to adjust the "pacing" of the learning to your daughter's capacity; you will not need to change any of the methodology.
You will need a copy of The Writing Road to Reading, a set of phonogram cards, a sounds CD to make certain you are teaching all of the sounds correctly, a primary spelling/vocabulary notebook. All of the necessary materials are available in kit form by calling Spalding Education International at 602-866-7801.