Playpennies

She is probably tired out and excited. I didn't notice a change from nursery, but when my youngest started school in September, I definitely notice that she is horrible in the evenings. Even though she spends less time at school than she did at nursery, the change of environment, routine, people is exhausting for her.
You just have to ride it out and understand that it's a new environment, new people, new toys, complete overload for her developing brain.
I'm sure in a few weeks she'll have got used to it and everything will be back to normal.

You don't say if it is nursery school or private daycare type nursery? I think nursery school and reception are actually far more exhausting for them than actual school (from year 1 up) because so much of their time is spent in free play. At nursery school, this meant effectively my son would simply spend all afternoon running up and down in all weather (they had waterproofs). They had a plastic pedal car and he liked to push it with one of the other children inside. Apparently, I'm told, he would do this for hours! It was no wonder he would come out tired and a little bit cranky. Also there's a correlation between how well behaved they are in class, and how horrible they when they get home! It is as if they've had this incredibly hard day being good, and when they get home they just want to shrug it off and relax and be cranky/rotten/a little terror.