What a difference the night makes

Sometimes she is fine all day and things go along very well and then the night comes and she looks for any reason at all to argue and fuss with me about anything.  I can tell she is looking to argue because once I agree with her she starts arguing the other point of view.  It is just so bizaar that there are no words.  Trying to walk that very thin line between parenting and supporting her through this struggle is just so very difficult.  I feel I have loss all control of my parenting and I am at the mercy of her moods.