It's not fair to A.  The slightest misbehavior when M has been acting out for days and I jump her.  I give her absolutely no room for error.  It's not fair to M.  I had let her out of her room tentatively to perform a simple task and in the middle of it, I told her to go back to her room with no explanation simply b/c A was beginning to throw a fit.  I can stay calm and focused when M is screaming at me and even when she is pounding on me but when things start to calm down, my fuse is short.  No, I didn't yell.  No, I didn't even fuss.  But I also didn't respond reasonably to the moment.  I could have easily yelled if either of the girls hadn't complied quickly.  It's not fair to either of them.