You are being cryptic, which is fair enough, but you do say that there is something going on and you are not sure if it is affecting her behaviour.
As a primary teacher, if I had a fiver for every time a child began to behave out of character and a parent denied there could be any out of school reason, only for a clear potential reason to later emerge, I would have retired a long time ago.
I remember one time when a previously happy, willing 8 year old child came in to my class on a Monday morning after a half term sulky, aggressive and refusing to do anything or to talk about what was wrong.
Extremely worried, I spoke to the mum at hometime who told me nothing had changed at home and she hadn't noticed any difference in him.
It was only the next day when another child tipped me off that I was able to tentatively ask the mum if anything had happened over the half term within the family? She then told me that she had thrown his dad out and moved her new boyfriend in to the home in the space of a week, 'but it hasn't affected him at all'.
So do please consider if this sudden change in behaviour is your child attempting to communicate or at least reacting to whatever it is that is going on. Chilren lack power in the adult world so don't always know how they are 'allowed' to respond, and they also often lack the vocabulary to explain how they are feeling. It comes out in different ways to the ways an adult might react.