This is a momentous strip: it marks the first appearance of imposing, wrathful Lucy. While all the Peanuts characters are complex, I think it's safe to say that this aspect of Lucy's personality will grow and become the most prevalent. It's certainly the most memorable.
It is interesting, I think, that so many of Lucy's most memorable attributes have arisen so rapidly, and over consecutive Sunday strips. Last week we saw a particularly extreme example of her fussiness. The week before saw the first really empathic treatment of her affection for Schroeder. Schulz and Peanuts puts forth the theory that Lucy's character (other than some early bits inspired by their young daughter) was adapted from Charles Schulz's wife Joyce. If we accepted that, then these strips might suggest some marital strife at the time.
It is my own theory that, when forced to create a lot of material over a long period, that it's impossible to avoid revealing and using aspects of your inner self, that eventually it comes out onto the page one way or another. However, I don't think it's necessarily the case that we can draw a direct line from Joyce to Lucy. I think a canny creator will obfuscate matters, and end up combining aspects from different people to write his characters. Still, the rapidity with which Lucy is approaching her mature form suggests (but certainly doesn't prove) Schulz had some kind of breakthrough or epiphany as he was drawing these strips.
Some meta stuff:
Sorry the blog has been slow lately. I've been trying to catch up with old projects (especially In Profundis), and it's left me a little bereft of energy. Am plugging away at them though.