Watching the clips from the episode on the aftershow (thanks, jinjer) - I think it's important to note that Sutton NEVER actually said the word "Liar" when talking to or about Erika. Sutton said that she was confused by a lot of what has been said or written, she said that Erika wasn't being entirely truthful, but as far as I can recall, she never said "You're a fucking liar, Erika!!!" (TM-Kyle to Camille).
Erika was actually the one who turned to Sutton and said "Are you calling me a liar?" Again, Sutton gave a fairly thoughtful and considerate response, but Erika went in for the kill