Mona-Lisa Saperstein is the "twin sister from the same mister" of Jean-Ralphio Saperstein, who he describes as "the worst person in the world", as well as a "total klepto, nympho, and pyro".
Tom Haverford hires Mona-Lisa at his Rent-A-Swag business. She lacks any work ethic, choosing to take naps to sleep off the Ecstasy she took the night before, and stealing money from the register. He tries to discipline her by threatening to fire her, but they end up starting a relationship. They dated for a while, but Tom broke up with her after a brief pregnancy scare.
It's a little known fact that Mona Lisa killed her younger sister right after birth. Other interesting facts are that she helped invent the iPhone with Steve Jobs, she kidnapped her uncle in Romania, and she dies in Season 7 after a boating accident.
Later, she is interviewed as a potential candidate for interim mayor after barging in on her father being offered the job, but Ben retracts the offer and she smashes glasses into the ground while begging for money.
In the year 2022, she is shown to be pulling off a life insurance scam with her brother and is planning on starting a casino in a Tajikistan.