At least for me, I'm Slvl 99 in NG+ and Reah doesn't appear anywhere. It seems that this bug is caused because I rang both bells without talking to Petrus. I read that the solution may be kill Capra Demon (I skipped him). I will try it and if it gets fixed I will post it in the wiki. I already have the Lordvessel and I was going to kill Nito when I didn't found Reah in ToG, and she never even appeared with her party at Firelink.
EDIT: Also I have the bug that causes that Undead Parish and Undead Burg are always infected with BPs, even when offline.
EDIT 2: Killing Capra Demon, and reloading the game 3 times, made Petrus appeared in Firelink telling me that he already lost his lady. So that is the solution
EDIT: Also I have the bug that causes that Undead Parish and Undead Burg are always infected with BPs, even when offline.
EDIT 2: Killing Capra Demon, and reloading the game 3 times, made Petrus appeared in Firelink telling me that he already lost his lady. So that is the solution