Honestly, if I were in your position, I would pony up for a private tutor for her, preferably someone who has experience with learning differences. If this is your weak area as well as hers, and you want serious progress in a limited timespan, I think a tutor would be the best solution.
I would definitely ditch Classical Writing. Although I like the program and have used it myself, it is big and complicated and does not sound like a good fit for you.
I would punt back to SWB's writing sequence from the books: oral narration, written narration, dictation, outlining, rewriting from outline then comparing to original, then short persuasive papers. At this point you could introduce the different kinds with a "Just the Facts Ma'am" resource such as Jensen's Format Writing. I taught a small group from that text and while I had to supplement here and there (it is not a professionally written text), it does teach the forms in a concise way.
If you could get an English tutor that understands learning differences AND would do writing SWB's way, I think you could make some real headway.
I have some but not extensive experience with learning differences, and I'm wishing you were local to me! I wish I could help.