If your right-brained child is learning the sounds that letters represent, why not jump right in and teach the sounds from within whole sight words? Since they are big-picture thinkers, right-brained learners are most successful when you start at what we'd typically consider to be the end and move toward the beginning.
One factor that exacerbates an already difficult situation is what happens in the brain when stress occurs. If you take a primarily right-brained learner, put her into a logic/sequential educational setting, the result is going to be stress for the child.
While our whole brain is engaged with anything we do - people are primarily Left- or Right-Hemisphere dominant in regards to how they learn. Our school system is structured to work for 15% of children.
This method of teaching cuts through the confusion of all the teaching details that did not help them and took them straight to the core of the learning that resulted in their being able to read, spell, and write. It is not the method that is incredible, but the capacity of the child’s brain to learn beautifully when we give it what it needs.
Testing can be a stressful time for both parent and child! The good news is that even if your child doesn’t perform as well as you had hoped, there is good reason to be optimistic! What we need to do is be prepared and be ready to carry out a good plan of action should test scores be less than stellar.