The series ends with I Know a Secret. She still writes stand alone books, though. If you like Rizzoli and Isles, you might like the Temperance Brennan series (Bones) by Kathy Reichs.
Iain Reid’s books are my favorite! I can’t recommend him enough.
I’m Thinking of Ending Things by Iain Reid
Foe by Iain Reid
Also, I really liked The Silent Patient and all Liane Moriarty
These are all different types of mystery/thrillers, but great in their own way.