No, Cass being unable to read is brought up in Batgirl #54. It's an excuse to break the bond between Babs and her by editorial mandate, probably, but you can't argue that Cass' problems are magically solved by this point. (And before that, Batgirl #53 is Steph as Robin, and #51-52... yeah, I got nothing on 51-52. It's got pretty art.)