Temper Tantrums

Today we started the school routine again after the long holiday break. Getting everyone awake (including me) was a chore. I should have know this afternoon wouldn't be any easier.
K4 has this nasty habit of releasing her daily stress on me as soon as she comes out of school. She's done this since preschool and it arrives in different forms - she's rude to her friend, she ignores me or throws a brief fit about something. Today she had a total meltdown - complete with crying and kicking as she rolled around on the grass outside of school.
I'm not exactly sure what started it. But it ended with her losing out on going to cub scouts tonight and having to go to bed early. The thing is, by grounding her from cub scouts, I've also grounded myself. I won't be able to go and see K3 get his awards. Definitely not smart of me, but at the time, I was grasping at straws trying to get through to her and I really thought the proposed grounding would move her in the right direction. I was wrong.
You would think after 4 kids that I would know exactly what to say, to do, and how I should have diffused the situation to begin with. With the middle two, they would have been off the grass and into the car before I got to two. Not K4. She's got a defiance only matched by the 17 year old.
And now, I have no choice but to follow through. If I relent and allow her to go, then I've set myself up for yet another tantrum of similar proportions. The funny thing about K4 is that she'll never admit defeat. When I said no cub scouts, her reply was that she really didn't want to go anyway. If I threaten the loss of toys, she tells me she's done with those toys. Right now, there's almost an entire Little People village in seclusion in the basement for that very reason.
And I'm left feeling guilty.
Some days it's hard to be a Mom.