How would I write an essay about the character traits of Lucetta in three paragraphs? The three paragraphs in the body should be structured as follows: first character trait with proof, second character trait with proof, discussion of foils.

Three traits that underlie Lucetta's character, seen in chapters 18 and 22, and that provide many of her motivations are that she is fond of scheming, she is a fraud, and she is self-serving.
Fond of Scheming: Hardy shows Lucetta to be scheming (given to plotting devious plans) in the letters she sends in chapters 18 and 22. In these, she reveals her different schemes for reintroducing herself to Henchard. Her letter in chapter 22 states that her scheme for first seeing him once she was settled in Casterbridge was to arrange a chance encounter with him in the streets and let her presence be a surprise. Not being endowed with patience, she changed her scheme and wrote the letter instead. "My first intention [scheme] was to keep you in ignorance...till [meeting] in the street; but I have thought better of this."
A Fraud: A fraud is someone who pretends that they are what they are not. She pretends to be a "Templeman," but she is a "Le Sueur." She pretends to be a lady of social position, but she only newly inherited her wealth. She pretends to be purely English, but she is very much French. "[My] ancestors in Jersey were as good as anybody in England.... [I] am quite an English person in my feelings and tastes."
Self-Serving: To be self-serving is to put personal needs ahead of others', as Lucetta quite clearly does with Elizabeth. A self-serving person expresses deepest emotion for their own struggles even in the face of greater suffering. In chapter 22, when Lucetta learns the depth of the breach between Elizabeth and Henchard, the hysteria she descends to illustrates her self-serving quality: "Lucetta looked blank...and burst into hysterical sobs. Here was a disaster—her ingenious scheme completely stultified."
https://www.gutenberg.org/files/143/143-h/143-h.htm