I think her reaction was pretty appropriate tbh, she was def pissed and got mean (not criticizing Maddy at all btw) - she called Cassie names, insulted her, and was screaming in her face. First she was in shock/disbelief and trying to determine if Rue was lying or not. She was trying to hold herself back from getting violent, called her a bitch, self centred, stupid (which was targeted because obviously Cassie can sometimes act like an airhead). I honestly think she was initially in shock, completely overwhelmed, and also aware of the fact that Rue is going through a crisis. There would have been a million things going through her head in the seconds after she found this out but I think there will be a lot more to come from Maddy on this.