In Fantastic Beasts: The Crimes of Grindelwald, a person is asking Flamel to go and fight.
We only hear the voice. Who is it?
FWIW you do see her portrait in the book as Flamel flicks through it.
FLAMEL flicks open another page. EULALIE HICKS, a young American professor at Ilvermorny, looks around, worried.
EULALIE What’s happening?
FLAMEL Exactly what he said would happen. Grindelwald rallies tonight at the cemetery, and there will be death!
EULALIE Then you gotta go!
FLAMEL (panicked) What? I haven’t seen action in two hundred years...
EULALIE You can do this, Flamel. We believe in you.
Fantastic Beasts: The Crimes of Grindelwald - The Original Screenplay, Scene 86