Board Thread:Online Discussion/@comment-71.201.232.121-20140615080558/@comment-24208078-20141116011645

If the Dragonborn sells or loses the starting thieves' guild gear, then upon receiving the "free upgrade to a piece of your choice" option, all future interactions with Tonilia will result in a dead end discussion of upgrading the gear and the Dragonborn will be unable to fence anything with her anymore.

That's copied from the article, you may have done that.