When 2 becomes 3, INSTANTLY!

This is not going to be a funny or as interesting blog but oh well, posting it anyway. Wednesday night I felt really awful at work and started to realize my mastitis (an infection of the breast usually from nursing) was returning. I could tell I had a fever, I was worn down beyond usual, and my breast was hurting me! I decided to wake up and go to just my family doctor, and not have to call and see if I could get in to the midwife. Well, long story short doc didn't help called the midwife who was out of town, and she called me in some more antibiotics! Hopefully this doesn't cause the thrush to return! I decided to hang out at my parents till Big Daddy came home since I was just too worn out. We came home and within 15 minutes the neighbor let her daughter cross the street to play with Gary! She is 6 but they do play nice most of the time. They were playing for a while and she wanted to see the baby so she came over and was looking at Cara. Well, Gary started pushing her a bit and telling her to play with him and I had to intervene and tell him we don't push our friends. Eventually, he had to sit because he would not listen! Gary and Olivia started to play again and they were on his swing set going down the slide. Olivia started running up the ladder and sliding down and running back to the ladder and taking Gary off the step he was on and running up again her self and back down. Eventually Gary got upset and yelled "I want to go up the ladder too", so I thought this would make her stop. Instead she continued to do it so Gary tried to start up the ladder faster he got to the third step and she climbed up and grabbed him and threw him off onto the ground. I jumped up and didn't yell but spoke very stern to her and said, "Olivia that was not nice!" I picked up Gary who was crying to console him, and she just froze. She just stood by the swing and wouldn't move. I tried to remain as calm as I could but the situation could have been more serious than it was. I didn't know what to do or what one does in a situation like that! How do you discipline somone else's child without becoming the "bad guy"? I don't know if she ended up telling her mom I was mean or what, and I certainly don't want her mom to think I am mean to her daughter. I never told the mom when she came over to get her either! Which my friend Heather is right I should have told her! I just didn't want her to think I was saying her daughter was bad or anything! OHHHH the trials of being a Mommy! So what do others reading this think?