Lucy's being pleased at her own orneriness is interesting. Being happy that she's difficult to be around is a very Lucy attitude. This might be overthinking a joke somewhat, but it does point the way to her increasing willfulness.
In this strip, Lucy is alone but she's still talking. Her speech is more like her thoughts than things she is actually saying. This is akin to the theater trope where characters turn and address the audience, unheard by others in the scene. Overturning this, later on there will be strips in which a character actually overhears another character's internal dialogue, which could be taken to mean that either Schulz is playing around with the convention, or that his characters really do frequently talk to themselves.
