The Equalizer 3 includes a brief cameo from Susan Plummer, and here's how Melissa Leo's character returns. The third installment of Denzel Washington's action franchise features almost no returning characters from the previous films outside his Robert McCall. The Equalizer 3 focuses entirely on a new story with a new set of characters. However, the movie does include some notable connections to the previous installments, including a brief appearance by Melissa Leo's Susan Plummer, that helps connect to the events of The Equalizer 3's ending.

https://screenrant.com/the-equalizer-3s-susan-plummer-cameo-explained/