Dr. Mengers was played by Barbara Steele in the movie Piranha.
She was once the lover of Dr. Hoak and worked in the same field like him. Now she works for the government. She, like Colonel Waxman, wants to keep the Piranhas alive for future wars and underestimates them, when they are set free. However, she was prepared to endanger lots of people in an attempt to keep them a secret while dealing with them and contributes to the massacre by the Piranhas later.
After the disaster she becomes responsible of the following investigation assuring the public that the threat is over. It is implied she will blame everything on Colonel Waxman to save herself.