I'm sick of my freind and this?

That sounds very insensitive of them. Try discussing with your other friends and sit your friend Katie down, alone, without Matt and have a discussion. And be very careful that you don't make it appear like you all ganged up on her. If she gets easily pissed off and becomes defensive, let her know if she wants sometime to cool off and rethink the stuff. Later, have a follow up convo again.