People are jumping to conclusions here.
She's not a brocon, her brother was basically her father so it is normal for her to feel any woman was below him. Therapy, it works, people.
Regarding the messages, I feel it is someone who is coming hard at her after she made the mistake of opening up about her troubles with her husband. If she was having a affair, why would she be so distraught about the guy basically going "I love you!" ? I know I am jumping to conclusions too, but I feel people are too quick into assuming every female character is a cheater regardless of the context.
She wants to protect her brother, but she has a history of overreacting to his partners, so now she's powerless to do anything because of her own choices.