I wanted to fill you in. First, I did speak to her rather seriously in the moment, but instead of yelling I got right down on her level and talked to her in a stern voice. I also had her get out a dust pan and clean up the hair. This was the immediate consequence of her action, which I think is a good life lesson: if you make a mess, you have to clean it up, and if you do something that someone has specifically asked you not to do, they are going to be annoyed.
Next, following the advice of Red and others, I put away the scissors, making a big point of telling everyone that I was pointing them away because Mary had cut her hair. Now, when she wants to use scissors for school work or crafts, which is often, she has to ask for them, and she gets it, because when she asks she always says "May I use the scissors and I am not going to cut my hair." This is also a great life lesson: if you do something that you have been asked not to do, you lose trust and the privileges that go along with trust, in this case free use of the scissors, but this could easily apply to the car, staying home alone, etc, as they get older.
I also did not even out her hair, as I have finally realized that Mary LOVES haircuts. The first time the girls cut their hair, I did not make a huge deal out of it, but I took them outside right away and cut their hair straight across the back. I did this because I was trying to avoid the inappropriate level of anger that I expressed when poor PT cut his hair when he was 3. The hair cut turned out to be a punishment for Holly (5), who was hoping to grow her hair long, but a reward for Mary, who enjoyed the one on one time with mom and the cozy feeling of having me brush her hair. As for the cosmetic issue, I just make her wear a headband all the time since that hides the one side she cut off.
The final blow came today, when her brothers went for haircuts at the actual barber shop. Mary begged for a hair cut, and I had the presence of mind to say that she could not get a haircut (and the lollipop that follows) because she had cut her own hair. In about six weeks, when it is time for another haircut, if we have been incident free, I will make a big point of saying that she does get to go for a haircut now because she has not been cutting her hair.
Now, I want to address the comment that said that this was just a safety issue. I disagree. It does matter to me that my kids have a generally neat appearance, and that was one part of it, but much more important to me was the discipline at stake. The first time around, it was a mistake, Mary had never been told not to cut her hair. By the third and fourth time it was just clear that either she was really pushing buttons or I was just not getting through to her, or both.
One comment reminded us that discipline is not just about keeping order in a busy household, but that we are teaching virtues that our children will need to be successful adults. I hope that my children will learn to obey me so that they will be safe as teens, when drugs, cars, and other difficult choices occur. They will need self control (discipline), and obedience to a higher authority (the law of the land, the rules in college, God) to function as adults.
This idea of character training really helped me, it was as though I had forgotten. I was only thinking about how I could get my daughter to stop cutting her hair, and frankly I was loosing the will to fight. Once I realized how much was at stake in her formation, however, I understood that this was one of many small tests that she and I would go through on the road from here to adulthood. I want my children to feel safe and loved and supported by me, but also to know that my rules are just and reasonable and that disobedience has consequences.
Also, of course, I do need to keep order in the short term, with five kids running around I just cannot have people cutting things willy-nilly, and I really don't want to be spending money on extra haircuts.
Speaking of money, I am thinking of giving my children a bit more money and letting that play a role in the consequences of things -- if she had to pay for a haircut with money that she had to earn, for example, or even just to pay for the headbands, that might have made a difference. I think that this will work really well with kids over 7, who seem to be too old for "time out" (except when they really just need a cooling off period).
I think that the haircutting was also symptomatic, so I have taken some initiatives --
-- trying to catch John and Mary doing good and complement them
--trying to make sure that they are not unsupervised for long stretches of time, I was mistaken as to how much freedom they were ready to handle
--trying to respond to small infractions with a time-out rather than letting them get away with things out because I am distracted
--singing Mary a bedtime song. I had gotten a bit rushed about bedtime, but I figure if she was so desperate for a haircut it may be that she just needs a bit more snuggle in each day. I have lost my lap, and she was a lap sitter, so I do need to attend to her need for physical affection from me.
Thanks to all who commented, you really helped me to work this through and get to a good place!