Kids cut hair, it's like it's in their gene's or something. K's hair in her 4 year old picture was below her waist and dried in slightly loose long curls, It was beautiful. She cut it 7 times over the next 3 months.
The first time she cut it was at Head Start with the safety scissors while doing crafts. She cut the entire left side of her hair off even with her left ear. It was still long behind the ear so I just trimmed it short on both sides in front of her ears.
The next time she cut her hair was at the farm while we were house sitting for my FIL while he was traveling. He had scissors in the oddest places and we missed a pair of them. She cut a huge chunk out of he back middle, again,I could cover it up with just a bit of a trim.
The next time she cut it was again at Head Start. She had a plasti-band ponytail holding her front hair out of her face and she took the scissors and cut straight down in front of the plasti-band. So, when I took it out that evening all the hair came out in the band and she looked like a Cockatiel bird on top. I was so distraught I puked and left for about an hour to get myself under control.
Her b-day is in the Fall and in the late Winter we had pictures made and her hair was so short on top it wouldn't lay down without lots of hairspray and hair gel. The pictures turned out fine but I look back and think "What could I have done differently"? There was nothing. Putting the scissors up did nothing, she found scissors other places. Spanking did nothing, it was an impulse and kids don't have very good impulse control, it's a learned skill. it comes with age.
My BFF has a daughter just 3 1/2 months older than K and she just cut her hair for the first time last week, at 7 years old. It looks awful too but she likes it, just loves that it sticks up straight on top. Her mom slicks it down with hair gel and puts a headband on it to keep it looking somewhat normal.
There is nothing that you could do to keep her from cutting her hair, anyone who says different doesn't understand the impulses of children.It was bound to happen.
I say talk to her again, maybe ground her from her favorite toys for the day after school with the understanding that she is not allowed to have scissors in her hands unless she has direct supervision by an adult.
You also have the opportunity to teach her that the consequences of telling the truth gets less consequences than being untruthful. You can decide about that but I would absolutely give a punishment for lying.
The other time she cut hair...we had just paid actual money to get J his first haircut to a boy cut. It was adorable, for about an hour, she cut his hair with my pinking shears from my sewing machine drawer. The sewing machine, serger, and ironing board are all strictly off limits, but if she had even slipped the tiniest bit he would have had a scar and stitches.