As a child, Obiageli shatters her water jar when she's returning from the stream, first laughing, then crying over this as she makes her way back to the family compound. She's goofing off when it happens, which shows that she's really just a normal kid who wants to have fun.

Why can't Ezinma carry her father's chair to the wrestling match things fall apart?

Because this is the order of Okonkwo's wives. Why can't Ezinma carry her father's chair to the wrestling match? She is a girl, it is the job of the boy to carry his father's chair.

Why was Okonkwo uncomfortable at Celebration?

He does not particularly like feasts, because the idleness that they involve makes him feel emasculated. Okonkwo's frustration at this idleness causes him to act violently, breaking the spirit of the celebration.