I hate to be the first answerer when my advice is possibly not going to be exactly what you are looking for. I find that teaching spelling--specifically--especially for older student and adults, today, is a bit of a waste of time.
My advice is to encourage this student to read, read, read. Also, incorporate the use of a word processor in her work. I do not consider ABC check to be a crutch, but rather a pretty useful tool for most adults (esp. in the professional world) to rely on for improved spelling.