Monica Vespucci is a lawyer and a vampire aficionado. She works at the same law firm as Catherine, and is close enough friends with her to be in charge of her bachelorette party. We meet Monica for the first time in Guilty Pleasures.
When Anita first meets Monica she wears her hair short and expertly cut, and has a dark health-club tan and perfect makeup. She wears a white silk blouse with a high, flared collar, and a button that says "Vampires are People too."
In The Killing Dance we learn that Monica's hair is auburn, her hair is still short and styled, and her makeup is still perfect, although the tan has faded around the edges. She is also visibly pregnant. Anita suspects that the one real fur coat in the clothing pile belongs to Monica on the basis that she "liked being close to dead things".
In Guilty Pleasures Monica initially comes off scatterbrained and only starts arranging Catherine's bachelorette party the morning of the day in question, calling Anita to ask her to be the designated driver, and arranging her to pick Monica and Catherine up after work. The three of them make up the whole party, as Monica claims everyone else was busy since it was such short notice. After dinner she takes them to a vampire strip club where she's a regular enough customer to have her own table, and is very much into the whole show. Eventually we learn that she is part of a plot to blackmail Anita into solving a series of vampire murders with Catherine's life at stake if Anita refuses, and the whole evening has been a setup for that purpose. When Anita threatens to kill Monica if Catherine ends up hurt, Monica is smugly certain that the vampires will bring her back as one of them, even if this is inconsistent with the series lore of how vampires are made. Anita assures Monica there won't be enough left of her to bring anything back once Anita is done, and Monica finally takes the threat seriously. Later, Monica drops Phillip off at Animators, Inc., and we learn from him that she's now afraid of Anita, but we don't see her again in person.
Monica isn't mentioned in The Laughing Corpse, but is presumably at least attending or more likely actively involved in the briefly mentioned wedding, possibly even as one of the bridesmaids, since Anita hasn't revealed to Catherine what kind of person Monica really is. We later learn that Anita can't figure out how to do so without revealing some unlawful acts of her own that would conflict with Catherine's morals.
In The Killing Dance we see Monica again in a dinner party thrown by Catherine, and the narrative claims--probably in error, considering the wedding--that Anita hasn't seen Monica since the events of Guilty Pleasures. It's been almost a year, and in the meantime Monica has seemingly lost her fear of Anita, and has married Robert, and they have managed to accidentally conceive a baby together with the help of a hot tub and a lot of sex, although they have another week to wait before they can test the baby for Vlad syndrome. Anita knows or at least suspects that Robert and Monica are going to report the events of the party to Jean-Claude. Later in the book Anita is taken to a crime scene that turns out to be for Robert's murder. After Anita realizes this she recommends that Monica won't be told over phone since she's pregnant, but flatly refuses to be the one to break the news to Monica. Tammy Reynolds does, once Monica gets home, and Monica is understandably hysterical and refuses to believe Robert is really dead. She goes into premature labor and almost loses the baby, and Anita holds her hand through the contractions while waiting for Catherine to arrive to the hospital to take over bedside sitting as an actual friend. Monica is eventually sedated, even if that's not a great option while pregnant. Later, Jean-Claude promises that Monica and their child will "want for nothing". In the epilogue we learn that the baby is due in August, three months from the main events of the books, and that the amnio came back clean of Vlad's syndrome. Apparently Monica also thinks that she's actual friends with Anita now, and calls her Auntie Anita. Anita isn't thrilled with either of these things.
Later in the series Anita and her live-in-sweeties often look after the kid when Monica is on business trips, since a vampire isn't very useful for picking up a kid from preschool or taking him into dance lessons during daylight hours.
Monica and Robert's home is in Countryside Hills within Creve Coeur, which is a nice, upscale, older neighborhood. The house is a typical one story suburban ranch house, although with a special feature that the yard is surrounded by brick walls as tall as the house walls. There's a wrought iron gate at the curved entrance in Mediterranean style. The yard has a stone path and square, rock-edged flowerbeds full of rosebushes, and a somewhat excessive amount of floodlights illuminating the area.
There's a screen in the front door. The living room is narrow but long, and has a TV and video center at the end. Two short hallways lead off the living room at right angles, and a dining room directly off of the first room. When Anita visits the place as a crime scene there's an open door that reveals carpeted stairs leading to a finished basement. One of the hallways leads into a second, smaller living room with a fireplace. That room is more boxlike, but the far wall is entirely brick, and Anita feels that it makes the room cozier. There's an open doorway to the left that leads to the kitchen, and the wall between the rooms has a pass-through on the top half, like an in-house window without a glass. The next room from the second living room is obviously new at Anita's visit, and hasn't got the final paint yet. There are sliding glass doors for the left-hand wall and an already usable hot tub that takes up most of the floor space. Yet another hallway leads away from the tub, also under construction, and leads into another, larger bathroom that is likewise not entirely finished. There's a carved wooden door at the end of the hall, made of new light-colored oak wood. Behind that door is a bedroom with a king-size bed and a bureau complete with a large mirror at the right-hand wall. On Anita's visit the bed has purple satin sheets and a lot of pillows. There's enough floor space for Robert to lay spreadeagled on the floor. Somewhere nearby there's also a nursery waiting for the upcoming birth.