Has it been 4 weeks since school started?
Could be she is over the newness of it. She is realizing, this was not just a temporary thing.
She could also be really tired. It takes a lot of energy to pay attention and behave all day long. The recess helps, but they are used to being able to play what they want. Make sure she is getting enough sleep. Maybe move up her bed time by 15 to 30 minutes.
She may also miss being home. We all need to remember that when our young children are in school all day, they want to be home in the afternoon and evenings. Not running around doing errands and taking more classes. They love the comfort of their own homes.
Maybe a once a week activity or a Saturday morning activity..
This falls in the "normal" behavior and reaction to school.
Send surprises in her lunch box, little notes, funny drawings.. Maybe a special treat that you do not usually send.
Just remind her of the fun stuff. OOo, you do not want to miss today, your lunch buddy "Stacy" will miss you.
OOO, today is music class, be sure to remember what you learn in there. I want to hear all about it!
Recess should be fun today, it is not raining!
I sent you a surprise in your lunch box.. Let me know this afternoon if you liked it.