Do you know approximately when Lucinda Lee Plunkett was born or where? I'm betting she was born at least few decades before 1998, or you're a child prodigy. I have the book "Ten Thousand Plunketts" by Emma Plunkett Ivy written in 1969... will do look ups for you when you find her parents. It certainly doesn't cover all the Plunkett family lines in America, but it's worth a look.
Enjoy your hunting.