We had a major blow up at our house last night.

When I went to pick the kids up from daycare, the assistant manager at the daycare came to me and said “SD11 is hanging with the WRONG boys here. SD11 and BD12 have been arguing all day. They broke a controller for one of the game systems. SD11 has been following BD12 around.”
The following around bothered me because just Friday evening at our family meeting we told them when you are angry to walk away from the other person. I know how SD11 can be aggravating to say the least.
So I called DH at work and advised him of the situation. He became very angry (I’m not sure with me or the situation) and said that SD11 couldn’t go to the birthday party that evening that they had both been invited to. We go home to get ready to take BD12 to the party. The next thing I know DH is screeching into the driveway and bursting into the house. He goes straight into the room with SD11 and slams the door. After about 10 minutes he comes out very angry and visibly shaken saying loudly over and over “I don’t know what to do. I don’t know what to do.” I left and took BD12 to the party. When I came back that’s when things got interesting. DH tells me that “something has to give” that he can’t take this anymore. We call SD11 into the room and DH confronts her in front of me. She starts telling us what she believes happened. She said that “she could see how BD12 thought that she was following her but she really wasn’t. Plus why would I follow her when I know she’s mad?” DH & I both said “to aggravate her”. I feel that she knew the whole time what she was doing but she knows how to play on her dad….that’s just my opinion. She also said that the “following” didn’t occur directly after the argument. At any rate, DH is at a loss for words at this point. Torn between believing his angel and knowing what the “truth” to the story was. When I picked BD12 up from the party she says that yes in fact the “following” did happen right after the argument and that when SD11 entered the room she would look directly at BD12 and smile. DH and I stay up for awhile discussing what the next plan of action should be. He says that this was an argument that they should have settled on their own without us. I say that we should have gotten involved because not only were the rules established at the family meeting but the daycare manager thought that it was big enough to tell me about.
Was I wrong? Did he act in haste by not letting SD11 attend the b-day party? By calling him did I pressure him into making a decision in haste?
Does anyone have opinions on this at all?