I have a moderately autistic son, and after trying many, many programs with him, I have found that All About Spelling has been the best approach. I also love a little phonogram video put out by the Lee County school system, which I have played each morning for both my autistic son and his younger brothers. It is a great little daily drill, and may help the sounds for each letter "stick" for your daughter, as the approach is so multi-sensory. Look to the left of this page for "Spalding DVD": http://pat.leeschools.net/Helpful%20Websites.htm
Michele