User blog comment:Morganaforever/Morgana's torturer in 5x08/@comment-5674726-20121117214304/@comment-5674726-20121117215111

"She even thought Gwen knew!"

If Morgana thinks that Arthur knew, and has now been convinced that Guinevere didn't, it could have an effect on how she views Guinevere now. Her animosity towards Guinevere differs from her animosity towards other characters because Morgana freely admitted that it wasn't anything Guinevere has done, it's what she was going to do, namely become Queen, and even that is something that she'd do because of Arthur's choices.

It's possible that Morgana views Guinevere as the only redeemable one.