I used the BOB books as it was good practice for all the "exceptions" in the English language. But just level 2 and 3 with about 15-16 books in each set. I got them at Costco at least 15 months ago.
After level 3, they say, move on to Chapter books and there isn't too much that she cannot read -- in Chapter books. And I also think BOB books worked, like Dr. Seuss, in the repitition of what they were practicing. I didn't find that with so many Step Into Reading books, like her princess stories. They were simpler to read but she didn't gain much skill.