The lawsuit alleges Harper failed to notify Lombardo and producers in 2012 that her cancer returned. She allegedly began forgetting lines and slurring her speech during rehearsals, so the director urged her to see her doctor.
She learned her lung cancer had spread to her brain and she was forced to withdraw from the play.
The lawsuit says Harper intentionally hid her symptoms and it left Lombardo scrambling to find a replacement.
Lombardo the inconvenience cost him $500,000. He's suing her for an addition $1.5 million in damages.
Harper had previously filed a lawsuit against Lombardo, saying he failed to pay her for the remainder of her contract on the play, despite the fact that she had to withdraw.
Harper announced earlier this month that she's feeling well, despite lasting one year longer than doctors gave her to live.
Reports that the star was cancer-free, however, are inaccurate. "As I have stated on many occasions, I have Leptomeningeal Carcinomatosis (Lepto), lung cancer that has traveled to the meninges around my brain," said Harper, adding, "What all parties want to be made clear now is that while the Lepto has not spread, I am still not cured. I am a cancer patient, and I continue to fight with the hope that a cure may be just around the corner."